Section 2 Motor Research

*Somatosensory and Motor Research*

10.1007/s12070-018-1322-7

Jacobs J, Lempert T, et al.

fneur.2014.00265

2013. 676p

canal benign paroxysmal positional vertigo (PSCBPPV). Indian Journal of Otolaryngology and Head & Neck Surgery. 2019 Mar;**71**(1):99-103. DOI:

[18] Tavartkiladze GA. Guidelines for clinical audiology. Moskva: Meditsina;

[19] Lopez-Escamez JA, Dlugaiczyk J,

Accompanying symptoms overlap during attacks in Menière's disease and vestibular migraine. Frontiers in Neurology. 2014;**5**:265. DOI: 10.3389/

[20] Міschanchuk N, Sushro Y,

Buzunov V, Fedirko PH. Sensory organs. In: Cerdiuk A, Bebeshko V, Bazyra D, Yamashita S, editors. Chapter 18. Health Effects of the Chornobyl Accident-A Quarter of Century Aftermath. Kyiv-Nagasaki: DIA; 2011. pp. 491-532

[21] Zabolotnyi DI, Mishchanchuk NS. Vestibular and acoustic dysfunctions in clean-up workers of Chornobyl accident (30 years of follow-up). Problemy Radiacijnoyi Medytsynyі Radiobiologii.

[22] Barany R, Ibershoff AE. Physiology and Pathology of the Semicircular Canals; Being an Excerpt of the Clinical Studies of Dr. Robert Barany with Notes and Addenda Gathered from the Vienna Clinics. New York: P. B. Hoeber;

[23] Semmanaselvan K, Vignesh SS, Muthukumar R, Jaya V. Vestibular evoked myogenic potentials after Epleys manoeuvre among individuals with benign paroxysmal positional vertigo. Indian Journal of Otolaryngology and Head & Neck Surgery. 2019 Jun;**71**(2):195-200. DOI: 10.1007/

2016;**21**:218-237. (in Ukrainian)

**54**

1910. 66p

s12070-019-01581-6

**57**

**Chapter 4**

*Marina Todo*

**1. Introduction**

**Abstract**

Examination of New Parameters

To evaluate the excitability of the spinal motor neural function, F wave in evoked electromyogram is often used. As the dominant nerve to the muscle was electrically stimulated, retrograde action potentials are transmitted from the stimulation point to the anterior horn cells of the spinal cord. Action potentials that are regenerated in the anterior horn cells of the spinal cord are transmitted to the muscle in an anterograde manner, which are recorded at the muscle. From this route, because F wave can be measured from the whole body nerve, it has been used in various situations. Usually, it is characteristic that the waveform of F wave appears in variety. In other words, the same waveform does not appear in healthy people. However, the same waveform may appear when a certain disease occurs. It has been reported that the same waveform called "repeater F" appears in patients with neurological diseases. However, techniques and experience are required to analyze the waveform, and it is not widely used in clinical practice. This article will explain the F waves in terms of neurophysiology and investigate whether the

from F-Wave Waveform Using

Addition Averaging Method

averaging method can be applied to F-wave waveform analysis.

correlation coefficient, same waveform, F-wave parameters

**Keywords:** F-wave waveform, usefulness of the addition averaging method,

When we move, the electrical signals are generated in the brain through the spinal cord, and muscles contract, which causes movement. In the electrical signal transmission, although the function of the spinal cord is important, there is no consensus on the function (i.e., spinal cord excitability). The F wave which is an evoked electromyogram is one of the means to reflect the excitability of the spinal cord. Although the generation mechanism of the F wave will be described later, the F wave is characterized by various waveform shapes that can be usually recorded. On the one hand, in cases of spinal cord disease and cerebral infarction, the F wave with same shape may be recorded. Recently, due to these characteristics of the F wave, the excitability of the spinal cord has been utilized for grasping the pathological condition of neurological disorders. On the other hand, the analysis for the waveform of the F wave varies depending of the researcher, and the F wave appears in various ways; it has not yet been established as one evaluation. Hence, the ultimate objective is to establish an analysis method of waveform with low cost

## **Chapter 4**

## Examination of New Parameters from F-Wave Waveform Using Addition Averaging Method

*Marina Todo*

## **Abstract**

To evaluate the excitability of the spinal motor neural function, F wave in evoked electromyogram is often used. As the dominant nerve to the muscle was electrically stimulated, retrograde action potentials are transmitted from the stimulation point to the anterior horn cells of the spinal cord. Action potentials that are regenerated in the anterior horn cells of the spinal cord are transmitted to the muscle in an anterograde manner, which are recorded at the muscle. From this route, because F wave can be measured from the whole body nerve, it has been used in various situations. Usually, it is characteristic that the waveform of F wave appears in variety. In other words, the same waveform does not appear in healthy people. However, the same waveform may appear when a certain disease occurs. It has been reported that the same waveform called "repeater F" appears in patients with neurological diseases. However, techniques and experience are required to analyze the waveform, and it is not widely used in clinical practice. This article will explain the F waves in terms of neurophysiology and investigate whether the averaging method can be applied to F-wave waveform analysis.

**Keywords:** F-wave waveform, usefulness of the addition averaging method, correlation coefficient, same waveform, F-wave parameters

## **1. Introduction**

When we move, the electrical signals are generated in the brain through the spinal cord, and muscles contract, which causes movement. In the electrical signal transmission, although the function of the spinal cord is important, there is no consensus on the function (i.e., spinal cord excitability). The F wave which is an evoked electromyogram is one of the means to reflect the excitability of the spinal cord. Although the generation mechanism of the F wave will be described later, the F wave is characterized by various waveform shapes that can be usually recorded. On the one hand, in cases of spinal cord disease and cerebral infarction, the F wave with same shape may be recorded. Recently, due to these characteristics of the F wave, the excitability of the spinal cord has been utilized for grasping the pathological condition of neurological disorders. On the other hand, the analysis for the waveform of the F wave varies depending of the researcher, and the F wave appears in various ways; it has not yet been established as one evaluation. Hence, the ultimate objective is to establish an analysis method of waveform with low cost

and effort and to improve the versatility of the analysis method in clinical setting. I will explain the F waves in terms of neurophysiology and investigated whether the averaging method can be applied to F-wave waveform analysis. In this article, we will explain with a brief reference to the physiological aspects of the F-wave generation mechanism in order to understand waveform analysis more deeply. The same waveform appears in motor nerve demyelinating diseases and diseases involving degeneration of spinal anterior horn cells. However, the same criterion for waveforms may differ from each researcher. Therefore, we found the same criterion using the correlation coefficient. The usefulness of the addition averaging method in waveform analysis was examined using the reference value of the same waveform and will be introduced here.

## **2. Outbreak mechanism and characteristics of F wave**

F waves conduct retrogradely toward the center when a certain electrical stimulus is afforded to the α motor neuron (hereinafter αMN). Originally, the axon does not reach the cell body due to impedance mismatch (resistance Ω = V/I) at the axion hillock. Therefore, the spinal cord anterior horn cells do not refire and do not generate F waves. However, when spikes cross the axion hillock and reach the anterior horn cells of the spinal cord due to some effect, they propagate to the dendrites and generate SD (soma-dendritic) spikes there. This spike reaches the axion hillock that has escaped from the absolute refractory period and conducts the axon antegrade from there, resulting in compound muscle action potential (CMAP) evoked from the governing muscle [1]. Nerve fibers have an absolute refractory period of 1 ms, and if the spike returns during the period corresponding to the refractory period of the axion hillock, no F waves can be generated because they cannot be conducted antegrade. Also, αMN has a structure of antidromic inhibition via Renshaw cells. Antidromic inhibition takes 2 ms, and it takes 1 ms to return from the axion hillock to the spinal cord anterior horn cells. In other words, in order to generate the F wave, the spinal cord anterior horn cells must reignite and conduct to the periphery between 1 ms after the absolute refractory period of the axion hillock has ended and 2 ms before antidromic inhibition of Renshaw cells. Whether or not the axion hillock is out of the absolute refractory period is determined by slight timing differences, and this is thought to significantly affect the incidence of F waves [1, 2]. In addition, the following three conditions are considered in which the F wave is likely to occur: (1) the hyperpolarized state in the cells increases the time required for conduction to the dendrites, which makes it easier to avoid the absolute refractory period of the axion hillock; (2) reduction of the absolute refractory period; and (3) excessive depolarization of the axon lowers the threshold level, making spikes more likely to occur with small stimuli [1] (**Figure 1**).

**59**

coding) [7].

*Examination of New Parameters from F-Wave Waveform Using Addition Averaging Method*

Although the F wave is conducted antegrade by refiring of the spinal cord horn cells and can be recorded, refiring does not occur in all neurons. Furthermore, the probability of firing the same cell with each electrical stimulation is usually low, and re-excitation occurs only once every 10–100 times [1]. Komori et al. reported that 1406 F waves were evoked by a total of 1957 electrical stimuli in 10 cases, which consisted of 1160 waveforms, of which 1033 (89.1%) had only 1 occurrence [3]. F waves can be evoked from most motor nerves, but the nerves used mainly for examination are the median nerve, ulnar nerve, and tibial nerve. Among these nerves, the ulnar and tibial nerves have a persistence close to 100%. In addition, the normal value of the F-wave persistence varies among researchers. For the median nerve, Komori and Suzuki et al. reported more than 40%, and Fisher et al. reported 79–100%, but if too high, they may suspect spasticity, a disorder of upper motor neurons. There are reports of peroneal nerves in the nerves targeted for F-wave tests, but it is said that there are cases of difficulties in Japanese people even in healthy subjects [4, 5]. In the background, Japanese people are suspected of having a potential peroneal neuropathy due to the unique Japanese culture such as sitting straight custom. Hirashima et al. reported that CMAP (M-wave) amplitude increased by peroneal nerve stimulation since 1995 [6] and examination of the

In the anterior horn of the spinal cord, there are neurons of various motor units (motor neuron pool). A motor unit is a unit composed of motor neurons, and the muscle fibers are governed by the neurons. One F wave appears due to the combination of refiring motor units. The F-wave waveforms are different due to the combination of the motor units and the timing shift; therefore, the F wave has a feature in which its waveforms appear in a variety. There are three types of motor units. The S type (slow-twitch type) is small in size and slow in contraction speed. The FF type (fast-twitch fatigable type) is large in size and fast in contraction speed but is easily fatigued. The FR type has characteristic between S type and FF type. When a person exerts, it depends on the number of motor units activated (recruitment) and the frequency of firing of motor neurons (rate

Henneman reports that there is a strong correlation between motor neuron size and recruitment order [8]. When exercising, there are rules that are mobilized in order from smaller motor units to larger motor units (size principle) [1, 2, 7]. Small motor neurons have a low stimulus threshold and are easy to fire even with weak input. The percentage of motor units varies from muscle to muscle. Enoka reported that 92.5% of S-type motor neurons and 7.5% of FR-type motor neurons dominated in gastrocnemius muscles. Similarly, the musculus interossei dorsales pedis and triceps brachii muscle were dominated mostly by small motor neurons [9]. When humans exert their power, fluctuations in rate coding, in addition to recruitment of motor units, have a great effect, too [10, 11]. For example, in a study by Moritz et al., as the muscle contraction strength of the musculus interossei dorsales pedis of the hand was gradually increased, the rate coding of firing and the number of motor units increased, and the contraction strength reached 60% or more (against maximum contraction strength). At 60% or more contraction, most of the work was done only by increasing the rate coding. In the case of F wave, it has no effect on one waveform, but F wave treats the average value of the waveform obtained by 16 or more stimuli. At that time, the rate coding of the same motor unit

*DOI: http://dx.doi.org/10.5772/intechopen.91758*

peroneal nerve is now being examined.

**3. Relationship between F wave and motor unit**

with respect to the number of stimulations is reflected [12].

**Figure 1.** *F-wave generation mechanism.*

*Examination of New Parameters from F-Wave Waveform Using Addition Averaging Method DOI: http://dx.doi.org/10.5772/intechopen.91758*

Although the F wave is conducted antegrade by refiring of the spinal cord horn cells and can be recorded, refiring does not occur in all neurons. Furthermore, the probability of firing the same cell with each electrical stimulation is usually low, and re-excitation occurs only once every 10–100 times [1]. Komori et al. reported that 1406 F waves were evoked by a total of 1957 electrical stimuli in 10 cases, which consisted of 1160 waveforms, of which 1033 (89.1%) had only 1 occurrence [3]. F waves can be evoked from most motor nerves, but the nerves used mainly for examination are the median nerve, ulnar nerve, and tibial nerve. Among these nerves, the ulnar and tibial nerves have a persistence close to 100%. In addition, the normal value of the F-wave persistence varies among researchers. For the median nerve, Komori and Suzuki et al. reported more than 40%, and Fisher et al. reported 79–100%, but if too high, they may suspect spasticity, a disorder of upper motor neurons. There are reports of peroneal nerves in the nerves targeted for F-wave tests, but it is said that there are cases of difficulties in Japanese people even in healthy subjects [4, 5]. In the background, Japanese people are suspected of having a potential peroneal neuropathy due to the unique Japanese culture such as sitting straight custom. Hirashima et al. reported that CMAP (M-wave) amplitude increased by peroneal nerve stimulation since 1995 [6] and examination of the peroneal nerve is now being examined.

## **3. Relationship between F wave and motor unit**

In the anterior horn of the spinal cord, there are neurons of various motor units (motor neuron pool). A motor unit is a unit composed of motor neurons, and the muscle fibers are governed by the neurons. One F wave appears due to the combination of refiring motor units. The F-wave waveforms are different due to the combination of the motor units and the timing shift; therefore, the F wave has a feature in which its waveforms appear in a variety. There are three types of motor units. The S type (slow-twitch type) is small in size and slow in contraction speed. The FF type (fast-twitch fatigable type) is large in size and fast in contraction speed but is easily fatigued. The FR type has characteristic between S type and FF type. When a person exerts, it depends on the number of motor units activated (recruitment) and the frequency of firing of motor neurons (rate coding) [7].

Henneman reports that there is a strong correlation between motor neuron size and recruitment order [8]. When exercising, there are rules that are mobilized in order from smaller motor units to larger motor units (size principle) [1, 2, 7]. Small motor neurons have a low stimulus threshold and are easy to fire even with weak input. The percentage of motor units varies from muscle to muscle. Enoka reported that 92.5% of S-type motor neurons and 7.5% of FR-type motor neurons dominated in gastrocnemius muscles. Similarly, the musculus interossei dorsales pedis and triceps brachii muscle were dominated mostly by small motor neurons [9].

When humans exert their power, fluctuations in rate coding, in addition to recruitment of motor units, have a great effect, too [10, 11]. For example, in a study by Moritz et al., as the muscle contraction strength of the musculus interossei dorsales pedis of the hand was gradually increased, the rate coding of firing and the number of motor units increased, and the contraction strength reached 60% or more (against maximum contraction strength). At 60% or more contraction, most of the work was done only by increasing the rate coding. In the case of F wave, it has no effect on one waveform, but F wave treats the average value of the waveform obtained by 16 or more stimuli. At that time, the rate coding of the same motor unit with respect to the number of stimulations is reflected [12].

*Somatosensory and Motor Research*

and will be introduced here.

and effort and to improve the versatility of the analysis method in clinical setting. I will explain the F waves in terms of neurophysiology and investigated whether the averaging method can be applied to F-wave waveform analysis. In this article, we will explain with a brief reference to the physiological aspects of the F-wave generation mechanism in order to understand waveform analysis more deeply. The same waveform appears in motor nerve demyelinating diseases and diseases involving degeneration of spinal anterior horn cells. However, the same criterion for waveforms may differ from each researcher. Therefore, we found the same criterion using the correlation coefficient. The usefulness of the addition averaging method in waveform analysis was examined using the reference value of the same waveform

F waves conduct retrogradely toward the center when a certain electrical stimulus is afforded to the α motor neuron (hereinafter αMN). Originally, the axon does not reach the cell body due to impedance mismatch (resistance Ω = V/I) at the axion hillock. Therefore, the spinal cord anterior horn cells do not refire and do not generate F waves. However, when spikes cross the axion hillock and reach the anterior horn cells of the spinal cord due to some effect, they propagate to the dendrites and generate SD (soma-dendritic) spikes there. This spike reaches the axion hillock that has escaped from the absolute refractory period and conducts the axon antegrade from there, resulting in compound muscle action potential (CMAP) evoked from the governing muscle [1]. Nerve fibers have an absolute refractory period of 1 ms, and if the spike returns during the period corresponding to the refractory period of the axion hillock, no F waves can be generated because they cannot be conducted antegrade. Also, αMN has a structure of antidromic inhibition via Renshaw cells. Antidromic inhibition takes 2 ms, and it takes 1 ms to return from the axion hillock to the spinal cord anterior horn cells. In other words, in order to generate the F wave, the spinal cord anterior horn cells must reignite and conduct to the periphery between 1 ms after the absolute refractory period of the axion hillock has ended and 2 ms before antidromic inhibition of Renshaw cells. Whether or not the axion hillock is out of the absolute refractory period is determined by slight timing differences, and this is thought to significantly affect the incidence of F waves [1, 2]. In addition, the following three conditions are considered in which the F wave is likely to occur: (1) the hyperpolarized state in the cells increases the time required for conduction to the dendrites, which makes it easier to avoid the absolute refractory period of the axion hillock; (2) reduction of the absolute refractory period; and (3) excessive depolarization of the axon lowers the threshold level, making spikes more

**2. Outbreak mechanism and characteristics of F wave**

likely to occur with small stimuli [1] (**Figure 1**).

**58**

**Figure 1.**

*F-wave generation mechanism.*

From the above, it is necessary to adjust the rate coding of firing of units of various sizes according to the scene. When various units fire, they appear in the waveform of the F wave, and the rate coding is directly reflected in the persistence of the F wave. In other words, it can be said that the waveform and appearance persistence of the F wave reflect the motor unit. However, it has been reported that when the number of anterior horn cells decreases or degenerates due to spinal cord anterior horn cell disease or motor neuron damage, the firing of the same unit is biased and the F wave shows the same waveform. Evaluation the F wave reflecting the unit this way has the potential to lead to an objective evaluation of muscle output and voluntary motion.

## **4. F-wave parameters**

## **4.1 Latency (ms)**

Latency is the time taken of an electrical stimulation conduction to reach the spinal cord anterior horn cells and return to the dominant muscle. This parameter is most commonly used in clinical practice and is a highly reproducible index. In addition, the shortest rise latency in the recorded F wave is called the minimum latency, which reflects motor fibers with fast conduction time. Conversely, the longest rise latency is called the maximum latency, which reflects motor fibers with slow conduction times (**Figure 2**). The speed of conduction is said to be affected by height, limb length, and skin temperature. Speed of conduction is particularly reduced in diseases that affect the myelin of peripheral nerves (e.g., Guillain-Barre syndrome, Charcot-Marie-Tooth disease, etc.) [1].

## **4.2 Amplitude (μV)**

Amplitude represents the magnitude of the waveform. There are two types of measurement methods. The first is the baseline to peak amplitude. The second is the peak-to-peak amplitude of the negative and positive vertices (**Figure 3**). We used

**61**

**Figure 4.**

*Examination of New Parameters from F-Wave Waveform Using Addition Averaging Method*

the second peak-to-peak amplitude this time to analyze the waveform, including the positive wave. To normalize the amplitude of the F wave, the amplitude F/M ratio is expressed by the ratio divided by the peak-to-peak amplitude of the M wave when the maximal stimulation is given to the motor nerve. It is said that if the amplitude F/M ratio shows a value of 5% or more, the possibility of upper motor

Duration indicates the time from the rise of the amplitude of the F wave to its return to the baseline. However, depending on the waveform, the position to return to the baseline is unclear, and care must be taken when using this index because it may be affected by the experience value of the measurer. In the case of the median nerve, the location where the F wave is generated is on the baseline after the genera-

Persistence indicates the ratio of the appearance of the F wave to the total number of stimulations. Analysis of only one waveform is not sufficient because

tion of the M wave, so it is difficult to define the baseline (**Figure 4**).

*Cases where it is difficult to measure the duration of the median nerve.*

*DOI: http://dx.doi.org/10.5772/intechopen.91758*

neuropathy is suspected [13].

*A way to measure amplitude value.*

**4.3 Duration (ms)**

**Figure 3.**

**4.4 Persistence (%)**

*Examination of New Parameters from F-Wave Waveform Using Addition Averaging Method DOI: http://dx.doi.org/10.5772/intechopen.91758*

#### **Figure 3.**

*Somatosensory and Motor Research*

**4. F-wave parameters**

syndrome, Charcot-Marie-Tooth disease, etc.) [1].

**4.1 Latency (ms)**

**4.2 Amplitude (μV)**

From the above, it is necessary to adjust the rate coding of firing of units of various sizes according to the scene. When various units fire, they appear in the waveform of the F wave, and the rate coding is directly reflected in the persistence of the F wave. In other words, it can be said that the waveform and appearance persistence of the F wave reflect the motor unit. However, it has been reported that when the number of anterior horn cells decreases or degenerates due to spinal cord anterior horn cell disease or motor neuron damage, the firing of the same unit is biased and the F wave shows the same waveform. Evaluation the F wave reflecting the unit this way has the potential to lead to an objective evaluation of muscle output and voluntary motion.

Latency is the time taken of an electrical stimulation conduction to reach the spinal cord anterior horn cells and return to the dominant muscle. This parameter is most commonly used in clinical practice and is a highly reproducible index. In addition, the shortest rise latency in the recorded F wave is called the minimum latency, which reflects motor fibers with fast conduction time. Conversely, the longest rise latency is called the maximum latency, which reflects motor fibers with slow conduction times (**Figure 2**). The speed of conduction is said to be affected by height, limb length, and skin temperature. Speed of conduction is particularly reduced in diseases that affect the myelin of peripheral nerves (e.g., Guillain-Barre

Amplitude represents the magnitude of the waveform. There are two types of measurement methods. The first is the baseline to peak amplitude. The second is the peak-to-peak amplitude of the negative and positive vertices (**Figure 3**). We used

**60**

**Figure 2.** *Latency type.* *A way to measure amplitude value.*

the second peak-to-peak amplitude this time to analyze the waveform, including the positive wave. To normalize the amplitude of the F wave, the amplitude F/M ratio is expressed by the ratio divided by the peak-to-peak amplitude of the M wave when the maximal stimulation is given to the motor nerve. It is said that if the amplitude F/M ratio shows a value of 5% or more, the possibility of upper motor neuropathy is suspected [13].

#### **4.3 Duration (ms)**

Duration indicates the time from the rise of the amplitude of the F wave to its return to the baseline. However, depending on the waveform, the position to return to the baseline is unclear, and care must be taken when using this index because it may be affected by the experience value of the measurer. In the case of the median nerve, the location where the F wave is generated is on the baseline after the generation of the M wave, so it is difficult to define the baseline (**Figure 4**).

#### **4.4 Persistence (%)**

Persistence indicates the ratio of the appearance of the F wave to the total number of stimulations. Analysis of only one waveform is not sufficient because

**Figure 4.** *Cases where it is difficult to measure the duration of the median nerve.*

the F wave has different waveforms at each stimulus. Komori et al. reported that sufficient reproducibility was obtained with more than 50 stimuli [14]. Currently, Kimura et al. have generally analyzed using the average value of F waves obtained at least 16–30 times or more stimuli.

Others analyze the number of negative vertices of the waveform. There is also an index called Fchronodispersion which indicates the variation of latency from the difference between the minimum latency and the maximum latency.

## **5. Characteristics of disease and F-wave waveform**

Among peripheral neuropathies (neuropathies), abnormalities of F-wave waveform due to motor nerve disorders have been reported mainly by Kimura et al. [1, 15–19]. There are reports of Guillain-Barre syndrome [15–17], Charcot-Marie-Tooth disease [19], and diabetic neuropathy [20, 21], which are diseases in which motor nerves are predominantly impaired. There are reports related to spasticity, one of the pyramidal tract disorders [22–25]. In recent years, there have been many reports of amyotrophic lateral sclerosis that is an intractable disease in which both upper and lower motor neurons are degenerated [1, 2]. In neuropathy, demyelination of axon myelin sheaths inhibits jump conduction and slows the conduction speed. As a result, it is easy to obtain a result such as a delay in the rise latency and a decrease in the persistence of the F wave. These diagnoses can be determined by latency which has high reproducibility among F-wave parameters.

The authors focused on abnormal F waveforms in disorders involving upper motor neuron disorders and spinal cord anterior horn cell degeneration. In cases of spasticity among stroke, Suzuki et al. report that as the electrical stimulation intensity is increased, the waveform of the F wave appears more like the H wave as the degree of muscle tone and tendon reflex increases [26]. In addition, Suzuki et al. measured F waves obtained from the abductor of the thumb by median nerve stimulation in one case of cerebrovascular disease and compared the disease duration at 9 months, 52 months, and 70 months later. Meanwhile, physical therapy was given. As a result, they reported that as the duration of physiotherapy increased, the amplitude of F waves decreased, and the waveforms varied. In addition, improved hand muscle tone and voluntary motion. Komori et al. also reported that the amplitude of F waves increased with spasticity [25]. However, other researchers measured F waves when median nerve stimulation was applied to 14 stroke patients, and the latency and persistence were not significantly different between the non-paralyzed side and the paralyzed side. The persistence of motor unit has been reported to decrease significantly on the paralyzed side regardless of the degree of muscle tone [23, 27]. In the case of amyotrophic lateral sclerosis, atrophy of the anterior horn cells of the spinal cord reduces the number of motor units and the number of firing anterior horn cells, so the persistence decreases significantly, and the same waveform begins to appear [27]. Similarly, spinal and bulbar muscular atrophy (SBMA) has been reported to produce F-wave waveform with similar characteristics [28–30].

### **6. Regulation of the same waveform**

F waves with matching latency and amplitude values may appear when spasticity due to stroke or when atrophy of the spinal cord horn cells occurs, such as in ALS and SBMA. This is known as "repeater F." This repeater F is reported

**63**

**Table 1.**

*Results of the selection of the same waveform.*

*Examination of New Parameters from F-Wave Waveform Using Addition Averaging Method*

to significantly appear more in patients with diabetic polyneuropathy, ALS, carpal tunnel syndrome, ulnar neuropathy, and L5 radiculopathy than in healthy

**6.1 Regulation of the same waveform using correlation coefficient**

The authors examined the relationship between the results that three researchers familiar with F waves judged visually the same waveform and the results of the correlation coefficient calculated from the data [37]. The target waveform is a waveform of 30 shots derived from the musculus abductor pollicis brevis by median nerve stimulation of a healthy person for 5 trials. A total of 150 waveforms were prepared. We asked each researcher to select the same waveform in a separate room to avoid interference. The data processing method of the F wave was a moving average of three terms using Microsoft Excel. The correlation between the waveform after the moving average and the raw waveform was an extremely high value of R = 0.9963, which sufficiently reflects the raw waveform. Next, the correlation coefficients of all combinations of waveforms evoked by applying 30 electrical stimuli per trial were calculated. The waveforms visually judged the same wave-

The results showed that the same waveform was selected by the 2 individuals as 10 waveforms, of which 9 (90%) showed a correlation coefficient of 0.95 or more. Next, the waveforms selected by the three persons had two waveforms, and both waveforms showed a correlation coefficient of 0.95 or more. It was suggested that the number of correlation coefficients R = 0.95 may be one index of the same

However, one waveform judged to be the same waveform was recognized, although the correlation coefficient was 0.71. They were similar in waveform

The authors wondered how it is difficult to determine the consistency of the waveforms using only the amplitude value or the latency and how to judge the waveforms to be the same. Some studies report the same waveform as an analysis item, but few describe the judgment method in detail. Some of the methods described for determining the same waveform include the following: (1) a method of visual judging by superimposing recorded waveforms [3, 33], (2) a method of determining the correlation coefficient between waveforms at a value of 1.00 [34, 35], and (3) in recent years, some researchers have decided to develop their own analysis software [36]. There is a risk that the evaluation method can be used only by those who are familiar with F waves when using the visual observation to determine the same waveform, because the degree of match defined as the same

*DOI: http://dx.doi.org/10.5772/intechopen.91758*

waveform includes individual differences.

forms selected by two or more out of three people.

waveform when analyzing the waveform of the F wave (**Table 1**).

subjects [1, 2, 31, 32].

*Examination of New Parameters from F-Wave Waveform Using Addition Averaging Method DOI: http://dx.doi.org/10.5772/intechopen.91758*

to significantly appear more in patients with diabetic polyneuropathy, ALS, carpal tunnel syndrome, ulnar neuropathy, and L5 radiculopathy than in healthy subjects [1, 2, 31, 32].

The authors wondered how it is difficult to determine the consistency of the waveforms using only the amplitude value or the latency and how to judge the waveforms to be the same. Some studies report the same waveform as an analysis item, but few describe the judgment method in detail. Some of the methods described for determining the same waveform include the following: (1) a method of visual judging by superimposing recorded waveforms [3, 33], (2) a method of determining the correlation coefficient between waveforms at a value of 1.00 [34, 35], and (3) in recent years, some researchers have decided to develop their own analysis software [36]. There is a risk that the evaluation method can be used only by those who are familiar with F waves when using the visual observation to determine the same waveform, because the degree of match defined as the same waveform includes individual differences.

#### **6.1 Regulation of the same waveform using correlation coefficient**

The authors examined the relationship between the results that three researchers familiar with F waves judged visually the same waveform and the results of the correlation coefficient calculated from the data [37]. The target waveform is a waveform of 30 shots derived from the musculus abductor pollicis brevis by median nerve stimulation of a healthy person for 5 trials. A total of 150 waveforms were prepared. We asked each researcher to select the same waveform in a separate room to avoid interference. The data processing method of the F wave was a moving average of three terms using Microsoft Excel. The correlation between the waveform after the moving average and the raw waveform was an extremely high value of R = 0.9963, which sufficiently reflects the raw waveform. Next, the correlation coefficients of all combinations of waveforms evoked by applying 30 electrical stimuli per trial were calculated. The waveforms visually judged the same waveforms selected by two or more out of three people.

The results showed that the same waveform was selected by the 2 individuals as 10 waveforms, of which 9 (90%) showed a correlation coefficient of 0.95 or more. Next, the waveforms selected by the three persons had two waveforms, and both waveforms showed a correlation coefficient of 0.95 or more. It was suggested that the number of correlation coefficients R = 0.95 may be one index of the same waveform when analyzing the waveform of the F wave (**Table 1**).


However, one waveform judged to be the same waveform was recognized, although the correlation coefficient was 0.71. They were similar in waveform

#### **Table 1.**

*Somatosensory and Motor Research*

least 16–30 times or more stimuli.

the F wave has different waveforms at each stimulus. Komori et al. reported that sufficient reproducibility was obtained with more than 50 stimuli [14]. Currently, Kimura et al. have generally analyzed using the average value of F waves obtained at

Others analyze the number of negative vertices of the waveform. There is also an index called Fchronodispersion which indicates the variation of latency from the

Among peripheral neuropathies (neuropathies), abnormalities of F-wave waveform due to motor nerve disorders have been reported mainly by Kimura et al. [1, 15–19]. There are reports of Guillain-Barre syndrome [15–17], Charcot-Marie-Tooth disease [19], and diabetic neuropathy [20, 21], which are diseases in which motor nerves are predominantly impaired. There are reports related to spasticity, one of the pyramidal tract disorders [22–25]. In recent years, there have been many reports of amyotrophic lateral sclerosis that is an intractable disease in which both upper and lower motor neurons are degenerated [1, 2]. In neuropathy, demyelination of axon myelin sheaths inhibits jump conduction and slows the conduction speed. As a result, it is easy to obtain a result such as a delay in the rise latency and a decrease in the persistence of the F wave. These diagnoses can be determined by latency which

The authors focused on abnormal F waveforms in disorders involving upper motor neuron disorders and spinal cord anterior horn cell degeneration. In cases of spasticity among stroke, Suzuki et al. report that as the electrical stimulation intensity is increased, the waveform of the F wave appears more like the H wave as the degree of muscle tone and tendon reflex increases [26]. In addition, Suzuki et al. measured F waves obtained from the abductor of the thumb by median nerve stimulation in one case of cerebrovascular disease and compared the disease duration at 9 months, 52 months, and 70 months later. Meanwhile, physical therapy was given. As a result, they reported that as the duration of physiotherapy increased, the amplitude of F waves decreased, and the waveforms varied. In addition, improved hand muscle tone and voluntary motion. Komori et al. also reported that the amplitude of F waves increased with spasticity [25]. However, other researchers measured F waves when median nerve stimulation was applied to 14 stroke patients, and the latency and persistence were not significantly different between the non-paralyzed side and the paralyzed side. The persistence of motor unit has been reported to decrease significantly on the paralyzed side regardless of the degree of muscle tone [23, 27]. In the case of amyotrophic lateral sclerosis, atrophy of the anterior horn cells of the spinal cord reduces the number of motor units and the number of firing anterior horn cells, so the persistence decreases significantly, and the same waveform begins to appear [27]. Similarly, spinal and bulbar muscular atrophy (SBMA) has been reported to produce F-wave waveform with similar

F waves with matching latency and amplitude values may appear when spasticity due to stroke or when atrophy of the spinal cord horn cells occurs, such as in ALS and SBMA. This is known as "repeater F." This repeater F is reported

difference between the minimum latency and the maximum latency.

**5. Characteristics of disease and F-wave waveform**

has high reproducibility among F-wave parameters.

**62**

characteristics [28–30].

**6. Regulation of the same waveform**

*Results of the selection of the same waveform.*

but slightly different in latency when the actual raw waveforms were checked. Therefore, the latency was shifted by 0.625 ms until the negative peak matches with the visual confirmation; as a result the waveform showing a correlation coefficient of 0.71 showed a correlation coefficient of 0.96.

Although the waveforms were the same in this study, the different latencies suggested that the correlation coefficient was low. We thought that the slight shift in the rise latency was affected the time it took for the spike to occur in the spinal cord anterior horn excitation threshold. This time the evoked musculus abductor pollicis brevis is composed of 115–171 motor units, considering the possibility that the rise latency could be shifted due to the spatial relationship of the cell bodies when cells are similar in size during refiring. Komori et al. allow for differences in negative peak latencies up to 1 ms when comparing the reproducibility of F waves [38]. It may be necessary to consider such differences in latency when analyzing the same waveform.

## **7. Research using the addition averaging method**

An analysis method that takes into account the F wave, in which various waveforms appear, has not yet been established. In addition, there is a report on the F-wave method (F-MUNE) for estimating motor units using F waves. However, analysis requires time and effort, and versatility is poor at present [27, 39, 40]. Therefore, as stated in this introduction, we examined whether the averaging method is applicable to F waves to increase versatility by establishing simple analysis methods. The averaging method approaches 0 by averaging the waveforms that appeared in diversity with repeated stimuli. On the other hand, a waveform that appears at a fixed latency also appears as a waveform after overlapping and addition averaging [1]. In the case F wave appears in the diversification, the value become close to 0 when the addition averaging process is performed. The wave remains after the addition averaging process when the same waveform appears repeatedly. It may be possible to distinguish the same or similar waveforms if the addition averaging method is used to analyze the waveform of the F wave. However, there is a risk that the waveform may disappear due to a slight difference in latency when applying this addition averaging method to the analysis of the waveform of the F wave. Furthermore, meaning is still unclear what waveform is calculated by the addition averaging method, so we first examined the relationship between the averaging waveform and the raw waveform.

### **7.1 Previous research on waveform analysis using the addition averaging method**

Eisen et al. [13] first studied F waves using the addition averaging method. They addition averaged the F waves obtained by giving 32 electrical stimulations into the tibial nerve of cerebrovascular patients and compared them with that of the healthy subjects. The waveform after addition averaging reported that the duration and amplitude could be reproduced in both cerebrovascular and healthy subjects [13]. In Japan, Komori et al. focused on the latency of the negative peak in order to pursue an evaluation method that combines reproducibility and simplicity in order to promote clinical application of F wave. The waveform after adding the negative peaks manually (addition method) showed that the reproducibility of the waveform was 86.7% for the median nerve and 73.3% for the tibial nerve, even when measured on another day [38]. Next, they reported that the waveform obtained by the addition averaging method sufficiently reflected the waveform of the proven addition method [41]. Sakamaki et al. point out that such as F waves, when negative waves

**65**

**Figure 5.**

*Examination of New Parameters from F-Wave Waveform Using Addition Averaging Method*

and positive waves appear at the same latency, may be offset when the addition averaging method is used for waveforms that appear in diversity [42]. Hiratsuka et al.'s research also tried to use the addition averaging method, but the amplitude was significantly reduced, making analysis difficult [43]. There have been fewer studies using the addition averaging method for F-wave analysis since the first half of 1988 from this background. There are other reports that use the addition averaging method for the F-wave analysis items [44–46], but only the latency and duration reflect the raw waveform, and it is a difficult situation to establish these as

**7.2 Relationship between F-wave persistence and addition averaging waveform**

We reexamined the usefulness of the addition averaging method, taking into contents what Sakamaki pointed out. First, we examined whether the persistence of F waves needs to be considered for the median nerve since the persistence of F

The method measured the F wave at rest and calculated the coincidence rate between addition averaging waveform for all waveforms and averaging waveform reflecting only F-wave appearance waveform. Subjects were 99 healthy volunteers (55 males and 45 females) who agreed to the study with an average age of 23.3 ± 5.3 years. The F wave was obtained by electrically stimulating the median nerve of the non-dominant upper limb. From the measured F waves, the waveform after addition average of the "waveform data of 1 trial (30 shots) (thereafter, TW)" and "waveform data of only the F-wave appearance waveform (thereafter, AW)" was obtained using Microsoft Excel. Next, the correlation coefficient between the two waveforms after addition average values was calculated using CORREL function. This correlation coefficient indicates the coincidence rate. The reference value of the same waveform used the correlation coefficient of 0.95 from previous studies. Next, a scatter diagram from the data of the F-wave persistence of each subject is created, and the coincidence rate is calculated using single regression analysis. The coefficient of determination (R2) is calculated, and the variation is obtained. It is examined whether the coincidence rate depends on the persistence of F wave. 80/99 subjects had a correlation coefficient between TW and AW of 0.95 or more, accounting for 80% of the total. Among them 38 subjects showed a correlation coefficient of 1.00, representing 38% of the total. 19/99 subjects showed a correlation coefficient of

*A circle graph showing the correlation coefficient of two addition averaging waveforms.*

*DOI: http://dx.doi.org/10.5772/intechopen.91758*

waves differs for each nerve to be affected.

parameters.

*Examination of New Parameters from F-Wave Waveform Using Addition Averaging Method DOI: http://dx.doi.org/10.5772/intechopen.91758*

and positive waves appear at the same latency, may be offset when the addition averaging method is used for waveforms that appear in diversity [42]. Hiratsuka et al.'s research also tried to use the addition averaging method, but the amplitude was significantly reduced, making analysis difficult [43]. There have been fewer studies using the addition averaging method for F-wave analysis since the first half of 1988 from this background. There are other reports that use the addition averaging method for the F-wave analysis items [44–46], but only the latency and duration reflect the raw waveform, and it is a difficult situation to establish these as parameters.

#### **7.2 Relationship between F-wave persistence and addition averaging waveform**

We reexamined the usefulness of the addition averaging method, taking into contents what Sakamaki pointed out. First, we examined whether the persistence of F waves needs to be considered for the median nerve since the persistence of F waves differs for each nerve to be affected.

The method measured the F wave at rest and calculated the coincidence rate between addition averaging waveform for all waveforms and averaging waveform reflecting only F-wave appearance waveform. Subjects were 99 healthy volunteers (55 males and 45 females) who agreed to the study with an average age of 23.3 ± 5.3 years. The F wave was obtained by electrically stimulating the median nerve of the non-dominant upper limb. From the measured F waves, the waveform after addition average of the "waveform data of 1 trial (30 shots) (thereafter, TW)" and "waveform data of only the F-wave appearance waveform (thereafter, AW)" was obtained using Microsoft Excel. Next, the correlation coefficient between the two waveforms after addition average values was calculated using CORREL function. This correlation coefficient indicates the coincidence rate. The reference value of the same waveform used the correlation coefficient of 0.95 from previous studies. Next, a scatter diagram from the data of the F-wave persistence of each subject is created, and the coincidence rate is calculated using single regression analysis. The coefficient of determination (R2) is calculated, and the variation is obtained. It is examined whether the coincidence rate depends on the persistence of F wave. 80/99 subjects had a correlation coefficient between TW and AW of 0.95 or more, accounting for 80% of the total. Among them 38 subjects showed a correlation coefficient of 1.00, representing 38% of the total. 19/99 subjects showed a correlation coefficient of

*A circle graph showing the correlation coefficient of two addition averaging waveforms.*

*Somatosensory and Motor Research*

of 0.71 showed a correlation coefficient of 0.96.

**7. Research using the addition averaging method**

waveform and the raw waveform.

**method**

but slightly different in latency when the actual raw waveforms were checked. Therefore, the latency was shifted by 0.625 ms until the negative peak matches with the visual confirmation; as a result the waveform showing a correlation coefficient

Although the waveforms were the same in this study, the different latencies suggested that the correlation coefficient was low. We thought that the slight shift in the rise latency was affected the time it took for the spike to occur in the spinal cord anterior horn excitation threshold. This time the evoked musculus abductor pollicis brevis is composed of 115–171 motor units, considering the possibility that the rise latency could be shifted due to the spatial relationship of the cell bodies when cells are similar in size during refiring. Komori et al. allow for differences in negative peak latencies up to 1 ms when comparing the reproducibility of F waves [38]. It may be necessary to consider such differences in latency when analyzing the same waveform.

An analysis method that takes into account the F wave, in which various waveforms appear, has not yet been established. In addition, there is a report on the F-wave method (F-MUNE) for estimating motor units using F waves. However, analysis requires time and effort, and versatility is poor at present [27, 39, 40]. Therefore, as stated in this introduction, we examined whether the averaging method is applicable to F waves to increase versatility by establishing simple analysis methods. The averaging method approaches 0 by averaging the waveforms that appeared in diversity with repeated stimuli. On the other hand, a waveform that appears at a fixed latency also appears as a waveform after overlapping and addition averaging [1]. In the case F wave appears in the diversification, the value become close to 0 when the addition averaging process is performed. The wave remains after the addition averaging process when the same waveform appears repeatedly. It may be possible to distinguish the same or similar waveforms if the addition averaging method is used to analyze the waveform of the F wave. However, there is a risk that the waveform may disappear due to a slight difference in latency when applying this addition averaging method to the analysis of the waveform of the F wave. Furthermore, meaning is still unclear what waveform is calculated by the addition averaging method, so we first examined the relationship between the averaging

**7.1 Previous research on waveform analysis using the addition averaging** 

Eisen et al. [13] first studied F waves using the addition averaging method. They addition averaged the F waves obtained by giving 32 electrical stimulations into the tibial nerve of cerebrovascular patients and compared them with that of the healthy subjects. The waveform after addition averaging reported that the duration and amplitude could be reproduced in both cerebrovascular and healthy subjects [13]. In Japan, Komori et al. focused on the latency of the negative peak in order to pursue an evaluation method that combines reproducibility and simplicity in order to promote clinical application of F wave. The waveform after adding the negative peaks manually (addition method) showed that the reproducibility of the waveform was 86.7% for the median nerve and 73.3% for the tibial nerve, even when measured on another day [38]. Next, they reported that the waveform obtained by the addition averaging method sufficiently reflected the waveform of the proven addition method [41]. Sakamaki et al. point out that such as F waves, when negative waves

**64**

**Figure 6.** *A scatter plot showing the persistence of F wave and the coincidence rate.*

0.95 or less, accounting for 20% of the total (**Figure 5**). A scatter plot showing the persistence of F wave and the coincidence rate is presented in **Figure 6**.

The coefficient determination (R) was 0.53, indicating "somewhat correlated." The highest F-wave persistence was 60%, and the lowest value was 10% in the group that showed a concordance rate of 0.95 or less (thereafter, group A). The highest F-wave persistence was 100%, and the lowest value was 23% in the group that showed a concordance rate of 0.95 or higher (thereafter, group B) (**Figure 6**). The result we expected was that the higher the persistence of F waves, the higher the coincidence rate. However, those with a high coincidence rate and those with a low coincidence rate were recognized despite low persistence of F wave in group A and group B. Therefore, we confirmed the raw waveform of those with low persistence of F wave in both groups. Then, there were two factors that reduced the coincidence rate in Group A.

The first factor is that the persistence of F waves is significantly lower. The amplitude could be confirmed visually because the fewer the number of waveforms that appeared, the smaller the value to be divided. On the other hand, the amplitude value was lost because the denominator to be divided was large. From the above, it is considered that the coincidence rate of the two waveforms has a low value. This result is similar to the reported study of Hiratsuka et al. [43].

The second factor is that high-amplitude waveforms appear localized. It was considered that the addition averaging waveform of AW had a higher amplitude value and a lower coincidence rate because of appearing several high-amplitude waveforms. In group B, there were also two possible factors for the high coincidence rate despite the low persistence of F-wave appearance as in group A. The first factor is that the persistence of the F wave is around 50%, and the appearing waveform shows almost a similar waveform. The second factor is, even though the number of appearing waveforms was few, they were canceled out by the appearance of diversity which is also a characteristic of the F wave. As a result, we thought that the matching rate approached the baseline and showed a high value. We think that the tasks of making the persistence of F waves approach 100% using muscle contraction or evoked from tibial nerve are suitable when using addition averaging method to analyze F-wave waveform.

#### **7.3 Method of addition averaging**

#### *7.3.1 Normal or match of negative peak or match of rise latency*

Compared with the commonly used amplitude F/M ratio, the amplitude value of after addition averaging waveform showed about 1/2 of the value [41]. It is

**67**

of only one subject.

**Table 2.**

**8. Conclusions**

*Examination of New Parameters from F-Wave Waveform Using Addition Averaging Method*

considered to be the result of the overlap between the negative and positive waves as reported by Sakamaki and Takasu [42]. To avoid the reverse winding proposal, averaging was performed in three ways, and the ratio of amplitudes of addition averaging and the average of the values obtained for each stimulus were compared.

The three ways of performing the averaging method are described below:

2.A method of addition averaging after the match of negative peak.

3.A method of addition averaging after the match of rise latency.

1.A method of addition averaging the recorded F wave as it is (normal).

Subjects picked up and analyzed one subject who showed 100% persistence of F wave. The results are shown in **Table 2**. The error amplitude F/M ratio was 2.0%, and the measured value was 25.79 μV during normal addition averaging. Next, the error when matching the negative peak was 0.43%, and the measured value was 39.59 μV. Finally, the error when the rise latency was matched was 0.67%, and the measured value was 62.05 μV. From the above, in the case of one subject this time, the average is usually the closest to the raw data, but it is necessary to increase the number of subjects and pursue it because it is the result

At the present time, when using the addition averaging method for the F-wave

waveform analysis, (1) the constant criterion of the same waveform using the correlation coefficient should be 0.95, (2) the persistence of F waves when using the addition averaging method is at least 60% or more and (3) the normal addition averaging method has less error in the amplitude value compared to the raw data. However, all the contents described this time are the analysis results of F waves evoked by electrically stimulating "median nerve." Therefore, we will analyze the ulnar nerve, the tibial nerve, and the peroneal nerve in the same way as described at the beginning and examine the innervated nerves to which the addition averaging method is applicable. In addition, "cluster analysis" will be introduced to avoid pointing out the content of Sakamaki et al. In this analysis method, similar waveforms are collected to create a cluster. By carrying out the cluster analysis before the addition averaging, the similar waveforms can be classified, and the cancelation of the positive wave and the negative wave due to the variation in the latency can be avoided. In addition, you can see how many F-wave clusters make up one trial

*DOI: http://dx.doi.org/10.5772/intechopen.91758*

*Comparison of three addition averaging methods and average data.*

*Examination of New Parameters from F-Wave Waveform Using Addition Averaging Method DOI: http://dx.doi.org/10.5772/intechopen.91758*


#### **Table 2.**

*Somatosensory and Motor Research*

**Figure 6.**

0.95 or less, accounting for 20% of the total (**Figure 5**). A scatter plot showing the

The coefficient determination (R) was 0.53, indicating "somewhat correlated." The highest F-wave persistence was 60%, and the lowest value was 10% in the group that showed a concordance rate of 0.95 or less (thereafter, group A). The highest F-wave persistence was 100%, and the lowest value was 23% in the group that showed a concordance rate of 0.95 or higher (thereafter, group B) (**Figure 6**). The result we expected was that the higher the persistence of F waves, the higher the coincidence rate. However, those with a high coincidence rate and those with a low coincidence rate were recognized despite low persistence of F wave in group A and group B. Therefore, we confirmed the raw waveform of those with low persistence of F wave in both groups. Then, there were two factors that reduced the coincidence rate in Group A. The first factor is that the persistence of F waves is significantly lower. The amplitude could be confirmed visually because the fewer the number of waveforms that appeared, the smaller the value to be divided. On the other hand, the amplitude value was lost because the denominator to be divided was large. From the above, it is considered that the coincidence rate of the two waveforms has a low value. This

The second factor is that high-amplitude waveforms appear localized. It was considered that the addition averaging waveform of AW had a higher amplitude value and a lower coincidence rate because of appearing several high-amplitude waveforms. In group B, there were also two possible factors for the high coincidence rate despite the low persistence of F-wave appearance as in group A. The first factor is that the persistence of the F wave is around 50%, and the appearing waveform shows almost a similar waveform. The second factor is, even though the number of appearing waveforms was few, they were canceled out by the appearance of diversity which is also a characteristic of the F wave. As a result, we thought that the matching rate approached the baseline and showed a high value. We think that the tasks of making the persistence of F waves approach 100% using muscle contraction or evoked from tibial nerve are suitable when using addition averaging method to analyze F-wave waveform.

Compared with the commonly used amplitude F/M ratio, the amplitude value of after addition averaging waveform showed about 1/2 of the value [41]. It is

persistence of F wave and the coincidence rate is presented in **Figure 6**.

*A scatter plot showing the persistence of F wave and the coincidence rate.*

result is similar to the reported study of Hiratsuka et al. [43].

*7.3.1 Normal or match of negative peak or match of rise latency*

**66**

**7.3 Method of addition averaging**

*Comparison of three addition averaging methods and average data.*

considered to be the result of the overlap between the negative and positive waves as reported by Sakamaki and Takasu [42]. To avoid the reverse winding proposal, averaging was performed in three ways, and the ratio of amplitudes of addition averaging and the average of the values obtained for each stimulus were compared. The three ways of performing the averaging method are described below:

1.A method of addition averaging the recorded F wave as it is (normal).

2.A method of addition averaging after the match of negative peak.

3.A method of addition averaging after the match of rise latency.

Subjects picked up and analyzed one subject who showed 100% persistence of F wave. The results are shown in **Table 2**. The error amplitude F/M ratio was 2.0%, and the measured value was 25.79 μV during normal addition averaging. Next, the error when matching the negative peak was 0.43%, and the measured value was 39.59 μV. Finally, the error when the rise latency was matched was 0.67%, and the measured value was 62.05 μV. From the above, in the case of one subject this time, the average is usually the closest to the raw data, but it is necessary to increase the number of subjects and pursue it because it is the result of only one subject.

## **8. Conclusions**

At the present time, when using the addition averaging method for the F-wave waveform analysis, (1) the constant criterion of the same waveform using the correlation coefficient should be 0.95, (2) the persistence of F waves when using the addition averaging method is at least 60% or more and (3) the normal addition averaging method has less error in the amplitude value compared to the raw data.

However, all the contents described this time are the analysis results of F waves evoked by electrically stimulating "median nerve." Therefore, we will analyze the ulnar nerve, the tibial nerve, and the peroneal nerve in the same way as described at the beginning and examine the innervated nerves to which the addition averaging method is applicable. In addition, "cluster analysis" will be introduced to avoid pointing out the content of Sakamaki et al. In this analysis method, similar waveforms are collected to create a cluster. By carrying out the cluster analysis before the addition averaging, the similar waveforms can be classified, and the cancelation of the positive wave and the negative wave due to the variation in the latency can be avoided. In addition, you can see how many F-wave clusters make up one trial

during a case characteristic of F-wave waveform such as stroke with spasticity or ALS with atrophy of spinal cord horn cells.

## **Acknowledgements**

We are grateful to Dr. Suzuki and laboratory members for their helpful discussions.

## **Conflict of interest**

Nothing.

## **Author details**

Marina Todo Clinical Physical Therapy Laboratory, Kansai University of Health Sciences, Osaka, Japan

\*Address all correspondence to: todo@kansai.ac.jp

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**69**

*Examination of New Parameters from F-Wave Waveform Using Addition Averaging Method*

Muscle & Nerve. 2001;**24**(1):4-17. DOI: 10.1002/1097-4598(200101)24: 1<4::AID-MUS13>3.0.CO;2-F

[10] Desmedt J, Godaux E. Fast motor units are not preferentially activated in rapid voluntary contractions in man. Nature. 1977;**267**:717-719. DOI:

[11] Person R, Kudina L. Discharge frequency and discharge pattern of human motor units during voluntary contraction of muscle. Electroencephalography and Clinical Neurophysiology. 1972;**32**(5):471-483. DOI: 10.1016/0013-4694(72)90058-2

[12] Moritz C, Barry B, Pascoe M, et al. Discharge rate variability influences the variation in force fluctuations across the working range of a hand muscle. Journal of Neurophysiology. 2005;**93**(5):2449- 2459. DOI: 10.1152/in.01122.2004

[13] Eisen A, Odusote K. Amplitude of the F wave: A potential means of documenting spasticity. Neurology. 1979;**29**(9):1306-1309. DOI: 10.1212/

[14] Komori T, Hirose K, Tsubaki T. A study of F-wave technique on the number

of stimuli and the reproducibility. Clinical Electroencephalography. 1986;**28**(11):770-774 [in Japanese]

[15] Fraser J, Olney R. The relative diagnostic sensitivity of different F-wave parameters in various polyneuropathies. Muscle & Nerve. 1992;**15**(8):912-918. DOI: 10.1002/

[16] Kokubun N, Kuwabara S. Electrical diagnosis of Guillain-Barre syndrome. Clinical Electroencephalography. 2013;**41**(2):103-111. DOI: 10.11422/ jscn.41.103. [Translated from Japanese]

[17] Gordon P, Wilbourn A. Early electrodiagnostic findings in

wnl.29.9\_part\_1.1306

mus.880150808

10.1038/267717a0

*DOI: http://dx.doi.org/10.5772/intechopen.91758*

[2] Abe T. The characteristics of F-wave in neurological disorders. Japanese Journal of Clinical Neurophysiology. 2018;**46**(4):175-186. DOI: 10.11422/

Hirose K, et al. Variability of F-wave shape. Clinical Electroencephalography.

[5] Bischoff C, Stalberg E, Falk B, et al. Significance of A-waves recorded in routine motor nerve conduction studies. Electroencephalography and Clinical Neurophysiology. 1996;**101**(6):528-533. DOI: 10.1016/S0921-884X(96)96553-4

[6] Hirashima F, Shimizu T, Koike K, et al. Interdecadal changes of nerve conduction studies of lower limb in healthy Japanese subject. Japanese Journal of Clinical Neurophysiology. 2019;**47**(6):519-525. DOI: 10.11422/

[7] Roger M. Neuromechanics of Human Movement. Niigata, Japan: Nishimura Co., Ltd.; 2017. pp. 141-151 [in Japanese]

jscn.47.519 [in Japanese]

[8] Henneman E. Relation

science.126.3287.1345

between size of neurons and their susceptibility to discharge. Science. 1957;**126**(3287):1345-1347. DOI: 10.1126/

[9] Enoka R, Fuglevand A. Motor unit physiology: Some unresolved issues.

[1] Kimura J, Kohara N. Nerve Conduction and Electromyography Studies. 2nd ed. Tokyo, Japan: IGAKU-SHOIN Ltd.; 2018. pp. 65, 80-83, 90-104. DOI: 10.11477/mf.1416100783

[in Japanese]

**References**

jscn.46.175 [in Japanese]

[3] Komori T, Takahashi R,

1988;**30**(1):1-6 [in Japanese]

[4] Jin C, Baba M, Matsunaga M. A right-left difference in motor nerve conduction parameter in healthy young adults. Clinical [in Japanese] Electroencephalography. 2003;**45**:234-238 *Examination of New Parameters from F-Wave Waveform Using Addition Averaging Method DOI: http://dx.doi.org/10.5772/intechopen.91758*

## **References**

*Somatosensory and Motor Research*

**Acknowledgements**

**Conflict of interest**

Nothing.

discussions.

ALS with atrophy of spinal cord horn cells.

**68**

**Author details**

Clinical Physical Therapy Laboratory, Kansai University of Health Sciences,

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

during a case characteristic of F-wave waveform such as stroke with spasticity or

We are grateful to Dr. Suzuki and laboratory members for their helpful

\*Address all correspondence to: todo@kansai.ac.jp

provided the original work is properly cited.

Marina Todo

Osaka, Japan

[1] Kimura J, Kohara N. Nerve Conduction and Electromyography Studies. 2nd ed. Tokyo, Japan: IGAKU-SHOIN Ltd.; 2018. pp. 65, 80-83, 90-104. DOI: 10.11477/mf.1416100783 [in Japanese]

[2] Abe T. The characteristics of F-wave in neurological disorders. Japanese Journal of Clinical Neurophysiology. 2018;**46**(4):175-186. DOI: 10.11422/ jscn.46.175 [in Japanese]

[3] Komori T, Takahashi R, Hirose K, et al. Variability of F-wave shape. Clinical Electroencephalography. 1988;**30**(1):1-6 [in Japanese]

[4] Jin C, Baba M, Matsunaga M. A right-left difference in motor nerve conduction parameter in healthy young adults. Clinical [in Japanese] Electroencephalography. 2003;**45**:234-238

[5] Bischoff C, Stalberg E, Falk B, et al. Significance of A-waves recorded in routine motor nerve conduction studies. Electroencephalography and Clinical Neurophysiology. 1996;**101**(6):528-533. DOI: 10.1016/S0921-884X(96)96553-4

[6] Hirashima F, Shimizu T, Koike K, et al. Interdecadal changes of nerve conduction studies of lower limb in healthy Japanese subject. Japanese Journal of Clinical Neurophysiology. 2019;**47**(6):519-525. DOI: 10.11422/ jscn.47.519 [in Japanese]

[7] Roger M. Neuromechanics of Human Movement. Niigata, Japan: Nishimura Co., Ltd.; 2017. pp. 141-151 [in Japanese]

[8] Henneman E. Relation between size of neurons and their susceptibility to discharge. Science. 1957;**126**(3287):1345-1347. DOI: 10.1126/ science.126.3287.1345

[9] Enoka R, Fuglevand A. Motor unit physiology: Some unresolved issues.

Muscle & Nerve. 2001;**24**(1):4-17. DOI: 10.1002/1097-4598(200101)24: 1<4::AID-MUS13>3.0.CO;2-F

[10] Desmedt J, Godaux E. Fast motor units are not preferentially activated in rapid voluntary contractions in man. Nature. 1977;**267**:717-719. DOI: 10.1038/267717a0

[11] Person R, Kudina L. Discharge frequency and discharge pattern of human motor units during voluntary contraction of muscle. Electroencephalography and Clinical Neurophysiology. 1972;**32**(5):471-483. DOI: 10.1016/0013-4694(72)90058-2

[12] Moritz C, Barry B, Pascoe M, et al. Discharge rate variability influences the variation in force fluctuations across the working range of a hand muscle. Journal of Neurophysiology. 2005;**93**(5):2449- 2459. DOI: 10.1152/in.01122.2004

[13] Eisen A, Odusote K. Amplitude of the F wave: A potential means of documenting spasticity. Neurology. 1979;**29**(9):1306-1309. DOI: 10.1212/ wnl.29.9\_part\_1.1306

[14] Komori T, Hirose K, Tsubaki T. A study of F-wave technique on the number of stimuli and the reproducibility. Clinical Electroencephalography. 1986;**28**(11):770-774 [in Japanese]

[15] Fraser J, Olney R. The relative diagnostic sensitivity of different F-wave parameters in various polyneuropathies. Muscle & Nerve. 1992;**15**(8):912-918. DOI: 10.1002/ mus.880150808

[16] Kokubun N, Kuwabara S. Electrical diagnosis of Guillain-Barre syndrome. Clinical Electroencephalography. 2013;**41**(2):103-111. DOI: 10.11422/ jscn.41.103. [Translated from Japanese]

[17] Gordon P, Wilbourn A. Early electrodiagnostic findings in

Guillain-Barré syndrome. Archives of Neurology. 2001;**58**(6):913-917. DOI: 10.1001/a rchneur.58.6.913

[18] Rajabally Y, Srinivas V. Practical electrodiagnostic value of F-wave studies in chronic inflammatory demyelinating polyneuropathy. Clinical Neurophysiology. 2013;**124**(1):171-175. DOI: 10.1016/j.clinph.2012.05.019

[19] Christova L, Alexandrov A, Ishpekova B. Peripheral late waves in patients with hereditary motor sensory neuropathy. Electromyography and Clinical Neurophysiology. 1999;**39**(6):345-348

[20] Kohara N, Kimura J, Kaji R, et al. F-wave latency serves as the most reproducible measure in nerve conduction studies of diabetic polyneuropathy: Multicentre analysis in healthy subjects and patients with diabetic polyneuropathy. Diabetologia. 2000;**43**:915-921. DOI: 10.1007/ s001250051469

[21] Pan H, Jian F, Lin J, et al. F-wave latencies in patients with diabetes mellitus. Muscle & Nerve. 2014;**49**(6):804-808. DOI: 10.1002/ mus.24127

[22] Yamashita A, Suzuki T, Bunno Y. Characteristic appearances of the H-reflex and F-wave in the lower extremity with increased stimulus intensity in subjects with cerebrovascular disease. Rigakuryoho Kagaku. 2013;**28**(5):563-567. DOI: 10.1589/rika.28.563

[23] Naseri M, Petramfar P, Ashraf A. Effect of motor imagery on the F-wave parameters in hemiparetic stroke survivors. Annals of Rehabilitation Medicine. 2015;**39**(3):401-408. DOI: 10.5535/ arm.2015.39.3.401

[24] Hara Y. Paralysis due to upper neuron lesion and motor units: Physiological motor unit number decrement on the hemiparetic side in strokes. Clinical Electroencephalography. 2003;**45**(7):423-428 [in Japanese]

[25] Suzuki T, Bunno Y, Tani M, et al. F-wave waveform values based on the correlation coefficient of each waveform increased following improved voluntary movements in a patient with cerebrovascular disease: A case study with long-term follow-up. International Journal of Neurorehabilitation. 2016;**3**(2):1000206. DOI: 10.4172/2376-0281.1000206

[26] Suzuki T, Saitoh E, Tani M, et al. Characteristic appearances of the H-reflex and F-wave with increased stimulus intensity in patients with cerebrovascular disease. Electromyography and Clinical Neurophysiology. 2002;**42**(2):67-70

[27] Hara Y. The lower motor neuron impairment in the central nervous lesion. Japanese Journal of Rehabilitation Medicine. 2000;**37**(1):43-52. DOI: 10.2490/ jjrm1963.37.43 [in Japanese]

[28] Suzuki K, Katsuno M, Banno H, et al. CAG repeat size correlates to electrophysiological motor and sensory phenotypes in SBMA. Brain. 2008;**131**(1):229-239. DOI: 10.1093/ brain/awm289

[29] Hama T, Hirayama M, Hara T, et al. Discrimination of spinal and bulbar muscular atrophy from amyotrophic lateral sclerosis using sensory nerve action potentials. Muscle & Nerve. 2012;**45**(2):169-174. DOI: 10.1002/ mus.22291

[30] Ibrahim K, El-Abd M. Giant repeater F-wave in patients with anterior horn cell disorders. Role of motor unit size. American Journal of Physical Medicine & Rehabilitation.

**71**

*Examination of New Parameters from F-Wave Waveform Using Addition Averaging Method*

and waveform identification by investigators. International Journal of Neurorehabilitation. 2017;**4**(4):1000287. DOI: 10.4172/2376-0281.1000287

[38] Komotri T, Takahashi R, Hirose K, et al. The significance of F-wave negative peak for clinical application. Japanese Journal of Electroencephalography and

[in Japanese]

Electronmyography. 1989;**17**(3):255-262

[39] Doherty T, Komori T, Stashuk D, et al. Physiological properties of single thenar motor units in the F-response of younger and older adults. Muscle & Nerve. 1994;**17**(8):860-872. DOI:

[40] Stshunk D, Doherty T, Kassam A, et al. Motor unit number estimates based on the automated analysis of F-responses. Muscle & Nerve. 1994;**17**(8):881-890. DOI: 10.1002/

Hirose K, et al. F-wave analysis using signal averaging as a simple and reliable method. Japanese Journal of Electroencephalography and

Electronmyography. 1990;**18**(3):293-301

[42] Sakamaki S, Takasu T. Clinical and electrophysiological study of patients with prolonged F wave duration. Clinical Electroencephalography. 1988;**30**(1):7-11 [in Japanese]

[43] Hiratsuka H, Inoue Y, Tomonaga S, et al. Comparison of F wave and H wave on spastic hand. Orthopedics and Traumatology. 1986;**35**(1):237-239. DOI: 10.5035/nishiseisai.35.237 [in Japanese]

[44] Abe N, Okamoto N, Otani K, et al. A study of F wave conduction velocity in normal children. Clinical Electroencephalography. 1988;**30**(8):530-534 [in Japanese]

10.1002/mus.880170805

[41] Komotri T, Takahashi R,

mus.880170807

[in Japanese]

*DOI: http://dx.doi.org/10.5772/intechopen.91758*

10.1097/00002060-199709000-00006

[31] Mesrati F, Vecchierini M. F-waves:

[32] Maceod W. Repeater F waves: A comparison of sensitivity with sensory antidromic wrist-to-palm latency and distal motor latency in the diagnosis of carpal tunnel syndrome. Neurology. 1987;**37**(5):773-778. DOI: 10.1212/

[33] Peioglou-Harmoussi S, Fawcett P, Howe D, et al. F-responses: A study of frequency, sharp and amplitude characteristics in healthy control subject. Journal of Neurology, Neurosurgery, and Psychiatry. 1985;**48**(11):1159-1164. DOI: 10.1136/

[34] Komatsu N, Take N, Takamori K, et al. F-waves of healthy subjects elicited by voluntary movements of different muscle contraction strengths: Consideration of the type of F-wave waveforms. KANSAIRIGAKU.

2016;**16**:69-77. DOI: 10.11354/jkpt.6.69

[35] Suzuki T, Bunno Y, Tani M. et al, A new analysis method of F-waves to obtain "F-wave waveform values". SM Journal of Neurology and Neuroscience.

1997;**76**(4):281-287. DOI:

Neurophysiology and clinical value. Neurophysiologie Clinique. 2004;**34**(5):217-243. DOI: 10.1016/i.

neucli.2004.09.005

wnl.37.5.773

jnnp.48.11.1159

[in Japanese]

2016;**2**(1):1005

[36] Chroni E, Veltsista D,

Papapaulou C, et al. Generation of repeater F waves in healthy subjects. Journal of Clinical Neurophysiology. 2017;**34**(3):236-242. DOI: 10.1097/ WNP.0000000000000360

[37] Todo M, Suzuki T, Fukumoto Y, et al. Application of F-waveform for the effect of physical therapy relationship between the correlation coefficient of the f-wave waveforms

*Examination of New Parameters from F-Wave Waveform Using Addition Averaging Method DOI: http://dx.doi.org/10.5772/intechopen.91758*

1997;**76**(4):281-287. DOI: 10.1097/00002060-199709000-00006

*Somatosensory and Motor Research*

10.1001/a rchneur.58.6.913

Guillain-Barré syndrome. Archives of Neurology. 2001;**58**(6):913-917. DOI:

units: Physiological motor unit number decrement on the hemiparetic side in strokes. Clinical Electroencephalography. 2003;**45**(7):423-428 [in Japanese]

[25] Suzuki T, Bunno Y, Tani M, et al. F-wave waveform values based on the correlation coefficient of each waveform increased following improved voluntary movements in a patient with cerebrovascular disease: A case study with long-term follow-up. International Journal of Neurorehabilitation. 2016;**3**(2):1000206.

DOI: 10.4172/2376-0281.1000206

[26] Suzuki T, Saitoh E, Tani M, et al. Characteristic appearances of the H-reflex and F-wave with increased stimulus intensity in patients with cerebrovascular disease. Electromyography and Clinical Neurophysiology. 2002;**42**(2):67-70

[27] Hara Y. The lower motor neuron impairment in the central nervous lesion. Japanese Journal of Rehabilitation Medicine. 2000;**37**(1):43-52. DOI: 10.2490/ jjrm1963.37.43 [in Japanese]

[28] Suzuki K, Katsuno M, Banno H, et al. CAG repeat size correlates to electrophysiological motor and sensory phenotypes in SBMA. Brain. 2008;**131**(1):229-239. DOI: 10.1093/

[29] Hama T, Hirayama M, Hara T, et al. Discrimination of spinal and bulbar muscular atrophy from amyotrophic lateral sclerosis using sensory nerve action potentials. Muscle & Nerve. 2012;**45**(2):169-174. DOI: 10.1002/

[30] Ibrahim K, El-Abd M. Giant repeater F-wave in patients with anterior horn cell disorders. Role of motor unit size. American Journal of Physical Medicine & Rehabilitation.

brain/awm289

mus.22291

[18] Rajabally Y, Srinivas V. Practical electrodiagnostic value of F-wave studies in chronic inflammatory

[19] Christova L, Alexandrov A, Ishpekova B. Peripheral late waves in patients with hereditary motor sensory neuropathy. Electromyography

and Clinical Neurophysiology.

2000;**43**:915-921. DOI: 10.1007/

[21] Pan H, Jian F, Lin J, et al. F-wave latencies in patients with diabetes mellitus. Muscle & Nerve. 2014;**49**(6):804-808. DOI: 10.1002/

[22] Yamashita A, Suzuki T,

10.1589/rika.28.563

arm.2015.39.3.401

[23] Naseri M, Petramfar P,

[24] Hara Y. Paralysis due to upper neuron lesion and motor

Ashraf A. Effect of motor imagery on the F-wave parameters in hemiparetic stroke survivors. Annals of Rehabilitation Medicine. 2015;**39**(3):401-408. DOI: 10.5535/

Bunno Y. Characteristic appearances of the H-reflex and F-wave in the lower extremity with increased stimulus intensity in subjects with cerebrovascular disease. Rigakuryoho Kagaku. 2013;**28**(5):563-567. DOI:

[20] Kohara N, Kimura J, Kaji R, et al. F-wave latency serves as the most reproducible measure in nerve conduction studies of diabetic polyneuropathy: Multicentre analysis in healthy subjects and patients with diabetic polyneuropathy. Diabetologia.

1999;**39**(6):345-348

s001250051469

mus.24127

demyelinating polyneuropathy. Clinical Neurophysiology. 2013;**124**(1):171-175. DOI: 10.1016/j.clinph.2012.05.019

**70**

[31] Mesrati F, Vecchierini M. F-waves: Neurophysiology and clinical value. Neurophysiologie Clinique. 2004;**34**(5):217-243. DOI: 10.1016/i. neucli.2004.09.005

[32] Maceod W. Repeater F waves: A comparison of sensitivity with sensory antidromic wrist-to-palm latency and distal motor latency in the diagnosis of carpal tunnel syndrome. Neurology. 1987;**37**(5):773-778. DOI: 10.1212/ wnl.37.5.773

[33] Peioglou-Harmoussi S, Fawcett P, Howe D, et al. F-responses: A study of frequency, sharp and amplitude characteristics in healthy control subject. Journal of Neurology, Neurosurgery, and Psychiatry. 1985;**48**(11):1159-1164. DOI: 10.1136/ jnnp.48.11.1159

[34] Komatsu N, Take N, Takamori K, et al. F-waves of healthy subjects elicited by voluntary movements of different muscle contraction strengths: Consideration of the type of F-wave waveforms. KANSAIRIGAKU. 2016;**16**:69-77. DOI: 10.11354/jkpt.6.69 [in Japanese]

[35] Suzuki T, Bunno Y, Tani M. et al, A new analysis method of F-waves to obtain "F-wave waveform values". SM Journal of Neurology and Neuroscience. 2016;**2**(1):1005

[36] Chroni E, Veltsista D, Papapaulou C, et al. Generation of repeater F waves in healthy subjects. Journal of Clinical Neurophysiology. 2017;**34**(3):236-242. DOI: 10.1097/ WNP.0000000000000360

[37] Todo M, Suzuki T, Fukumoto Y, et al. Application of F-waveform for the effect of physical therapy relationship between the correlation coefficient of the f-wave waveforms

and waveform identification by investigators. International Journal of Neurorehabilitation. 2017;**4**(4):1000287. DOI: 10.4172/2376-0281.1000287

[38] Komotri T, Takahashi R, Hirose K, et al. The significance of F-wave negative peak for clinical application. Japanese Journal of Electroencephalography and Electronmyography. 1989;**17**(3):255-262 [in Japanese]

[39] Doherty T, Komori T, Stashuk D, et al. Physiological properties of single thenar motor units in the F-response of younger and older adults. Muscle & Nerve. 1994;**17**(8):860-872. DOI: 10.1002/mus.880170805

[40] Stshunk D, Doherty T, Kassam A, et al. Motor unit number estimates based on the automated analysis of F-responses. Muscle & Nerve. 1994;**17**(8):881-890. DOI: 10.1002/ mus.880170807

[41] Komotri T, Takahashi R, Hirose K, et al. F-wave analysis using signal averaging as a simple and reliable method. Japanese Journal of Electroencephalography and Electronmyography. 1990;**18**(3):293-301 [in Japanese]

[42] Sakamaki S, Takasu T. Clinical and electrophysiological study of patients with prolonged F wave duration. Clinical Electroencephalography. 1988;**30**(1):7-11 [in Japanese]

[43] Hiratsuka H, Inoue Y, Tomonaga S, et al. Comparison of F wave and H wave on spastic hand. Orthopedics and Traumatology. 1986;**35**(1):237-239. DOI: 10.5035/nishiseisai.35.237 [in Japanese]

[44] Abe N, Okamoto N, Otani K, et al. A study of F wave conduction velocity in normal children. Clinical Electroencephalography. 1988;**30**(8):530-534 [in Japanese]

[45] Takada T, Baba H, Tobita T, et al. Evaluation of the reproducibility of F-wave in relation to stimulating condition. Clinical Electroencephalography. 1993;**35**(5):302-309

[46] Tanaka S, Hachisuka K, Ogata H. The usefulness of automatic averaging tibial nerve F waves for assessment of spasticity in stroke hemiplegics. The journal of Japan Accident Medical Association. 1995;**45**(11):739-743

**73**

**Chapter 5**

Study

**Abstract**

*Yoshibumi Bunno*

strategy, stroke, neurorehabilitation

**1. Introduction**

Motor Imagery for

Neurorehabilitation: The F-Wave

The immediate enrollment in rehabilitation program and facilitation of the excitability of spinal motor neurons are very important for post-stroke patients. We previously suggested that persistence and the F/M amplitude ratio, indicator of the excitability of spinal motor neurons, were significantly increased during MI. Thus, MI has a greater effect on the excitability of spinal motor neurons. We also indicated that the imagined muscle contraction strength may not affect the excitability of spinal motor neurons. Further, kinesthetic imagery can more facilitate the excitability of spinal motor neurons. However, longer duration of MI may not affect the excitability of spinal motor neurons. Therefore, slight imagined muscle contraction strength may be sufficient to facilitate the excitability of spinal motor neurons, and duration and strategy of imagery should be considered in neurorehabilitation.

**Keywords:** motor imagery, F-wave, imagined muscle contraction strength, duration,

The excitability of the motor cortex is decreased after stroke along with damage to neural substrates, loss of sensory inputs, and disuse of the affected limb [1]. Further, the amplitude of motor evoked potentials (MEPs), obtained when transcranial magnetic stimulation (TMS) is applied over the primary motor cortex, is decreased [2]. At the spinal level, the excitability of spinal motor neurons is decreased in post-stroke patients during the acute phase [3, 4]. The excitability of central and spinal neural function is decreased after stroke. The highest level of functional recovery due to neuroplasticity, cortical reorganization, and regeneration occurs at about 4 weeks after stroke, and recovery reaches plateau within 3 months [5, 6]. Therefore, in post-stroke patients, the immediate enrollment in rehabilitation programs aiming to facilitate the corticospinal excitability, including the excitability of spinal motor neurons, should be important. Indeed, the early initiation of

rehabilitation programs can facilitate the recovery of motor function [6–8].

Motor imagery (MI) is a cognitive process creating specific motor actions within working memory without an actual movement [9]. MI allows patients who cannot volitionally perform movements, such as stroke, to mentally practice a motor task. Numerous neurophysiological studies have discussed the effect of MI on the central nervous system by using positron emission tomography, functional magnetic resonance imaging, and near-infrared spectroscopy [10–13]. The primary motor cortex,

## **Chapter 5**

*Somatosensory and Motor Research*

of F-wave in relation to

stimulating condition. Clinical Electroencephalography. 1993;**35**(5):302-309

[46] Tanaka S, Hachisuka K,

1995;**45**(11):739-743

[45] Takada T, Baba H, Tobita T, et al. Evaluation of the reproducibility

Ogata H. The usefulness of automatic averaging tibial nerve F waves for assessment of spasticity in stroke hemiplegics. The journal of Japan Accident Medical Association.

**72**

## Motor Imagery for Neurorehabilitation: The F-Wave Study

*Yoshibumi Bunno*

## **Abstract**

The immediate enrollment in rehabilitation program and facilitation of the excitability of spinal motor neurons are very important for post-stroke patients. We previously suggested that persistence and the F/M amplitude ratio, indicator of the excitability of spinal motor neurons, were significantly increased during MI. Thus, MI has a greater effect on the excitability of spinal motor neurons. We also indicated that the imagined muscle contraction strength may not affect the excitability of spinal motor neurons. Further, kinesthetic imagery can more facilitate the excitability of spinal motor neurons. However, longer duration of MI may not affect the excitability of spinal motor neurons. Therefore, slight imagined muscle contraction strength may be sufficient to facilitate the excitability of spinal motor neurons, and duration and strategy of imagery should be considered in neurorehabilitation.

**Keywords:** motor imagery, F-wave, imagined muscle contraction strength, duration, strategy, stroke, neurorehabilitation

## **1. Introduction**

The excitability of the motor cortex is decreased after stroke along with damage to neural substrates, loss of sensory inputs, and disuse of the affected limb [1]. Further, the amplitude of motor evoked potentials (MEPs), obtained when transcranial magnetic stimulation (TMS) is applied over the primary motor cortex, is decreased [2]. At the spinal level, the excitability of spinal motor neurons is decreased in post-stroke patients during the acute phase [3, 4]. The excitability of central and spinal neural function is decreased after stroke. The highest level of functional recovery due to neuroplasticity, cortical reorganization, and regeneration occurs at about 4 weeks after stroke, and recovery reaches plateau within 3 months [5, 6]. Therefore, in post-stroke patients, the immediate enrollment in rehabilitation programs aiming to facilitate the corticospinal excitability, including the excitability of spinal motor neurons, should be important. Indeed, the early initiation of rehabilitation programs can facilitate the recovery of motor function [6–8].

Motor imagery (MI) is a cognitive process creating specific motor actions within working memory without an actual movement [9]. MI allows patients who cannot volitionally perform movements, such as stroke, to mentally practice a motor task. Numerous neurophysiological studies have discussed the effect of MI on the central nervous system by using positron emission tomography, functional magnetic resonance imaging, and near-infrared spectroscopy [10–13]. The primary motor cortex, premotor area, supplementary motor area, prefrontal cortex, parietal lobule, cingulate area, cerebellum, and basal ganglia were activated during MI [10–13]. These brain areas were also activated during motor execution (ME), and thus the MI and ME have a common neural network. Further, the MEP amplitude was significantly increased during MI [2, 14, 15]. Therefore, MI can facilitate the excitability of the central nervous system.

However, the influence of MI on the excitability of spinal motor neurons is still unclear. A significant increase of the spinal motor neuron excitability was observed during MI [16, 17]. Our previous study also demonstrated a significant increase of the spinal motor neurons during MI of isometric thenar muscle activity at 50% maximal voluntary contraction (MVC) [18]. Conversely, previous studies demonstrated that excitability of spinal motor neurons is not changed during MI [14, 19, 20]. Additionally, Oishi et al. [21] identified three changing patterns (i.e., facilitation, suppression, and no change) in the excitability of spinal motor neurons during MI. These results of previous studies indicated that MI has various effects on the spinal motor neuron excitability. MI includes various components of perception, such as visual, auditory, kinesthetic, proprioceptive, and vestibular. Further, MI incorporates the spatial (e.g., direction and amplitude), temporal (e.g., synchronization and continuously), and dynamic (e.g., muscle tension) information relevant to the motor task. Therefore, the excitability of spinal motor neurons during MI may be different depending on what modality of MI will be chosen. Then, we investigated the excitability of spinal motor neurons during MI under various conditions, specifically imagined muscle contraction strength, duration, and sensory modality. One of the final goals of our group is to find the best conditions for MI to achieve the optimum outcome during the rehabilitation program. In the following sections, we introduce our previous researches and suggest the application of MI to rehabilitation.

## **2. The excitability of spinal motor neurons during MI at different imagined muscle contractions**

#### **2.1 Background and purpose**

Our research group previously reported that the excitability of spinal motor neurons was significantly increased during MI of isometric thenar muscle activity at 50% MVC [18]. In actual movement, the excitability of spinal motor neurons was increased linearly with muscle contraction strength [22]. If MI and ME share a common neural network, the excitability of spinal motor neurons increases linearly with imagined muscle contraction strength. Firstly, we aimed to investigate the excitability of spinal motor neurons during MI at different imagined muscle contraction strength. The excitability of spinal motor neurons during MI was assessed using the F-wave [23–26].

#### **2.2 About the F-wave**

The F-wave is compound action potentials resulting from the re-excitation (backfiring) of spinal anterior horn cells by an antidromic impulse following distal electrical stimulation of α motor neurons [27–29] (**Figure 1**). The F-wave amplitude was significantly increased when the corticospinal descending volley collides with the antidromic peripheral volley [30]. Therefore, the F-wave is considered to be a probe of the excitability of spinal motor neurons. Further, Rossini et al. [31] suggested that the F-wave is a reliable index of the excitability of spinal motor neurons, even when motor output is extremely minimal, as during MI.

**75**

**Figure 2.**

*F-wave recording status.*

*Motor Imagery for Neurorehabilitation: The F-Wave Study*

Firstly, we assessed the excitability of spinal motor neurons during MI at 10, 30, 50, and 70% MVC for 10 healthy adults (mean age = 28.7 ± 4.5 years). Secondly, we assessed the excitability of spinal motor neurons during MI at 50 and 100% MVC for 15 healthy adults (mean age = 25.3 ± 5.0 years). Written informed consent was obtained prior to participation. The study was approved by the Research Ethics Committee at Kansai University of Health Sciences and conducted in accordance

A Viking Quest Electromyography (EMG) machine version 9.0 (Natus Medical, Inc., Pleasanton, CA, USA) was used to record the F-wave. Participants were in supine posture on a bed and instructed to fix one's eyes on the display of a pinch meter (Digital indicator F304A, Unipulse Corp., Japan) (**Figure 2**).

*DOI: http://dx.doi.org/10.5772/intechopen.91834*

**2.3 Materials and methods**

with the Declaration of Helsinki.

*2.3.2 Apparatus and condition for the F-wave recording*

*2.3.1 Participants*

*Mechanism of the F-wave.*

**Figure 1.**

*Motor Imagery for Neurorehabilitation: The F-Wave Study DOI: http://dx.doi.org/10.5772/intechopen.91834*

**Figure 1.** *Mechanism of the F-wave.*

*Somatosensory and Motor Research*

central nervous system.

premotor area, supplementary motor area, prefrontal cortex, parietal lobule, cingulate area, cerebellum, and basal ganglia were activated during MI [10–13]. These brain areas were also activated during motor execution (ME), and thus the MI and ME have a common neural network. Further, the MEP amplitude was significantly increased during MI [2, 14, 15]. Therefore, MI can facilitate the excitability of the

However, the influence of MI on the excitability of spinal motor neurons is still unclear. A significant increase of the spinal motor neuron excitability was observed during MI [16, 17]. Our previous study also demonstrated a significant increase of the spinal motor neurons during MI of isometric thenar muscle activity at 50% maximal voluntary contraction (MVC) [18]. Conversely, previous studies demonstrated that excitability of spinal motor neurons is not changed during MI [14, 19, 20]. Additionally, Oishi et al. [21] identified three changing patterns (i.e., facilitation, suppression, and no change) in the excitability of spinal motor neurons during MI. These results of previous studies indicated that MI has various effects on the spinal motor neuron excitability. MI includes various components of perception, such as visual, auditory, kinesthetic, proprioceptive, and vestibular. Further, MI incorporates the spatial (e.g., direction and amplitude), temporal (e.g., synchronization and continuously), and dynamic (e.g., muscle tension) information relevant to the motor task. Therefore, the excitability of spinal motor neurons during MI may be different depending on what modality of MI will be chosen. Then, we investigated the excitability of spinal motor neurons during MI under various conditions, specifically imagined muscle contraction strength, duration, and sensory modality. One of the final goals of our group is to find the best conditions for MI to achieve the optimum outcome during the rehabilitation program. In the following sections, we introduce our previous researches and suggest the application of MI to rehabilitation.

**2. The excitability of spinal motor neurons during MI at different** 

Our research group previously reported that the excitability of spinal motor neurons was significantly increased during MI of isometric thenar muscle activity at 50% MVC [18]. In actual movement, the excitability of spinal motor neurons was increased linearly with muscle contraction strength [22]. If MI and ME share a common neural network, the excitability of spinal motor neurons increases linearly with imagined muscle contraction strength. Firstly, we aimed to investigate the excitability of spinal motor neurons during MI at different imagined muscle contraction strength. The excitability of spinal motor neurons during MI was assessed

The F-wave is compound action potentials resulting from the re-excitation (backfiring) of spinal anterior horn cells by an antidromic impulse following distal electrical stimulation of α motor neurons [27–29] (**Figure 1**). The F-wave amplitude was significantly increased when the corticospinal descending volley collides with the antidromic peripheral volley [30]. Therefore, the F-wave is considered to be a probe of the excitability of spinal motor neurons. Further, Rossini et al. [31] suggested that the F-wave is a reliable index of the excitability of spinal motor neurons,

even when motor output is extremely minimal, as during MI.

**imagined muscle contractions**

**2.1 Background and purpose**

using the F-wave [23–26].

**2.2 About the F-wave**

**74**

## **2.3 Materials and methods**

## *2.3.1 Participants*

Firstly, we assessed the excitability of spinal motor neurons during MI at 10, 30, 50, and 70% MVC for 10 healthy adults (mean age = 28.7 ± 4.5 years). Secondly, we assessed the excitability of spinal motor neurons during MI at 50 and 100% MVC for 15 healthy adults (mean age = 25.3 ± 5.0 years). Written informed consent was obtained prior to participation. The study was approved by the Research Ethics Committee at Kansai University of Health Sciences and conducted in accordance with the Declaration of Helsinki.

## *2.3.2 Apparatus and condition for the F-wave recording*

A Viking Quest Electromyography (EMG) machine version 9.0 (Natus Medical, Inc., Pleasanton, CA, USA) was used to record the F-wave. Participants were in supine posture on a bed and instructed to fix one's eyes on the display of a pinch meter (Digital indicator F304A, Unipulse Corp., Japan) (**Figure 2**).

**Figure 2.** *F-wave recording status.*

**Figure 3.** *F-wave recording condition.*

The skin impedance was cleaned with an abrasive gel (Nuprep® Skin Prep Gel; Weaver and Company, Inc., Aurora, CO, USA) to maintain below 5 kΩ. The room temperature was maintained at 25°C. A pair of silver EEG cup electrodes (10 mm diameter; Natus Medical, Inc., Pleasanton, CA, USA) was attached over the thenar muscles and the base of the first dorsal metacarpal bone (**Figure 3**).

The F-wave was evoked from the left thenar muscles by delivering supramaximal electrical stimuli to the left median nerve at wrist. Supramaximal stimulus intensity was determined to be 20% higher than the maximal stimulus intensity that could elicit the largest M-wave amplitude. Thirty electrical stimuli in each trial were delivered at a duration of 0.2 ms and frequency of 0.5 Hz. The sensitivity for the F-wave was set at 200 μV per division and a sweep of 5 ms per division. The bandwidth filter ranged from 20 Hz to 3 kHz.

## *2.3.3 Experimental protocol*

Firstly, to determine baseline of the excitability of spinal motor neurons, the F-wave was recorded during relaxation for 1 min (rest). After baseline of the F-wave recording, participants were instructed to learn isometric left thenar muscle activity at 50% MVC for 1 min with visual feedback. Specifically, participants press the sensor of a pinch meter by the left thumb and index finger at 50% MVC and keep the 50% MVC value numerically recorded on the display. For the MI trial, participants imagined isometric left thenar muscle activity at 50% MVC for 1 min (50% MI). After MI trial, the F-wave was recorded during relaxation for 1 min (post). This protocol was repeated for 10, 30, 70, and 100% MI conditions. Each condition was performed randomly on different days.

## **2.4 Data analysis for the F-wave**

The F-wave data in each trial were analyzed with respect to two parameters: persistence and the F/M amplitude ratio. The minimum peak-to-peak amplitude of F-waves was 20 μV [17, 32]. Persistence was defined as the number of detected F-wave responses to 30 electrical stimuli and expressed as percentage (%). Persistence reflects the number of backfiring spinal anterior horn cells [28, 29]. The F/M amplitude ratio was defined as the mean amplitude of all detected F-wave responses divided by the M-wave amplitude and expressed as percentage (%). The F/M amplitude ratio reflects the size, number, and synchronization of backfiring spinal anterior horn cells [29, 33]. Therefore, persistence and the F/M amplitude ratio indicate the excitability of spinal motor neurons.

**77**

**Table 1.**

*The F-wave under 10% MI condition.*

*Motor Imagery for Neurorehabilitation: The F-Wave Study*

*DOI: http://dx.doi.org/10.5772/intechopen.91834*

*2.5.1 The F-wave during 10–70% MI condition*

*2.5.2 The F-wave during 50 and 100% MI condition*

*2.6.1 The F-wave during 10–70% MI condition*

*2.6.2 The F-wave during 50 and 100% MI condition*

was significantly higher than rest (**Tables 6** and **7**).

strate significant differences among all MI conditions (**Table 5**).

IBM SPSS statistics version 26 (IBM Corp., Armonk, NY, USA) was used for statistical analysis. A nonparametric method was used for statistical analysis because the normality of obtained data was not confirmed by the Shapiro-Wilk test.

Persistence and the F/M amplitude ratio among three trials (rest, MI, and post) under each MI condition (10, 30, 50, and 70%) were compared using the Friedman

Persistence and the F/M amplitude ratio among three trials (rest, MI, and post) under each MVC MI condition were compared using the Friedman test and Scheffe's post hoc test. The relative values between two MI conditions were compared using

Persistence during MI under all MI conditions was significantly higher than the rest (**Tables 1**–**4**). The F/M amplitude ratio during MI under 10, 30, and 50% MI conditions was significantly higher than rest (**Tables 1**–**3**). The F/M amplitude ratio during MI under 70% MI condition was tended to be increased than rest (**Table 4**). The relative values of persistence and the F/M amplitude ratio did not demon-

Persistence during MI under the two MI conditions was significantly higher than rest (**Tables 6**, **7**). The F/M amplitude ratio during MI under the two MI conditions

We also calculated the relative value obtained by dividing the F-wave data during MI under four MI conditions by that at rest. The relative values among four MI conditions were compared using the Friedman test. The threshold for statistical

**2.5 Statistical analysis**

test and Scheffe's post hoc test.

significance was set at p = 0.05.

the Wilcoxon signed rank test.

**2.6 Results**

## **2.5 Statistical analysis**

*Somatosensory and Motor Research*

**Figure 3.**

*F-wave recording condition.*

The skin impedance was cleaned with an abrasive gel (Nuprep® Skin Prep Gel; Weaver and Company, Inc., Aurora, CO, USA) to maintain below 5 kΩ. The room temperature was maintained at 25°C. A pair of silver EEG cup electrodes (10 mm diameter; Natus Medical, Inc., Pleasanton, CA, USA) was attached over the thenar muscles and the base of the first dorsal metacarpal bone (**Figure 3**).

The F-wave was evoked from the left thenar muscles by delivering supramaximal electrical stimuli to the left median nerve at wrist. Supramaximal stimulus intensity was determined to be 20% higher than the maximal stimulus intensity that could elicit the largest M-wave amplitude. Thirty electrical stimuli in each trial were delivered at a duration of 0.2 ms and frequency of 0.5 Hz. The sensitivity for the F-wave was set at 200 μV per division and a sweep of 5 ms per division. The

Firstly, to determine baseline of the excitability of spinal motor neurons, the F-wave was recorded during relaxation for 1 min (rest). After baseline of the F-wave recording, participants were instructed to learn isometric left thenar muscle activity at 50% MVC for 1 min with visual feedback. Specifically, participants press the sensor of a pinch meter by the left thumb and index finger at 50% MVC and keep the 50% MVC value numerically recorded on the display. For the MI trial, participants imagined isometric left thenar muscle activity at 50% MVC for 1 min (50% MI). After MI trial, the F-wave was recorded during relaxation for 1 min (post). This protocol was repeated for 10, 30, 70, and 100% MI conditions. Each

The F-wave data in each trial were analyzed with respect to two parameters: persistence and the F/M amplitude ratio. The minimum peak-to-peak amplitude of F-waves was 20 μV [17, 32]. Persistence was defined as the number of detected F-wave responses to 30 electrical stimuli and expressed as percentage (%). Persistence reflects the number of backfiring spinal anterior horn cells [28, 29]. The F/M amplitude ratio was defined as the mean amplitude of all detected F-wave responses divided by the M-wave amplitude and expressed as percentage (%). The F/M amplitude ratio reflects the size, number, and synchronization of backfiring spinal anterior horn cells [29, 33]. Therefore, persistence and the F/M amplitude

bandwidth filter ranged from 20 Hz to 3 kHz.

condition was performed randomly on different days.

ratio indicate the excitability of spinal motor neurons.

*2.3.3 Experimental protocol*

**2.4 Data analysis for the F-wave**

**76**

## *2.5.1 The F-wave during 10–70% MI condition*

IBM SPSS statistics version 26 (IBM Corp., Armonk, NY, USA) was used for statistical analysis. A nonparametric method was used for statistical analysis because the normality of obtained data was not confirmed by the Shapiro-Wilk test.

Persistence and the F/M amplitude ratio among three trials (rest, MI, and post) under each MI condition (10, 30, 50, and 70%) were compared using the Friedman test and Scheffe's post hoc test.

We also calculated the relative value obtained by dividing the F-wave data during MI under four MI conditions by that at rest. The relative values among four MI conditions were compared using the Friedman test. The threshold for statistical significance was set at p = 0.05.

## *2.5.2 The F-wave during 50 and 100% MI condition*

Persistence and the F/M amplitude ratio among three trials (rest, MI, and post) under each MVC MI condition were compared using the Friedman test and Scheffe's post hoc test. The relative values between two MI conditions were compared using the Wilcoxon signed rank test.

## **2.6 Results**

## *2.6.1 The F-wave during 10–70% MI condition*

Persistence during MI under all MI conditions was significantly higher than the rest (**Tables 1**–**4**). The F/M amplitude ratio during MI under 10, 30, and 50% MI conditions was significantly higher than rest (**Tables 1**–**3**). The F/M amplitude ratio during MI under 70% MI condition was tended to be increased than rest (**Table 4**).

The relative values of persistence and the F/M amplitude ratio did not demonstrate significant differences among all MI conditions (**Table 5**).

## *2.6.2 The F-wave during 50 and 100% MI condition*

Persistence during MI under the two MI conditions was significantly higher than rest (**Tables 6**, **7**). The F/M amplitude ratio during MI under the two MI conditions was significantly higher than rest (**Tables 6** and **7**).



#### **Table 2.**

*The F-wave under 30% MI condition.*


#### **Table 3.**

*The F-wave under 50% MI condition.*


#### **Table 4.**

*The F-wave under 70% MI condition.*


**79**

**Table 8.**

**2.7 Discussion**

**Table 6.**

**Table 7.**

extrapyramidal tracts.

*Motor Imagery for Neurorehabilitation: The F-Wave Study*

*The persistence and F/M amplitude ratio under 50% MI condition.*

*The persistence and F/M amplitude ratio under 100% MI condition.*

The relative values of the persistence and F/M amplitude ratio did not demon-

Both persistence and the F/M amplitude ratio significantly increased during MI under all five MI conditions. Previous studies demonstrated that various brain regions, including the primary motor cortex, premotor area, supplementary motor area, prefrontal cortex, parietal lobule, cingulate area, cerebellum, and basal ganglia, contribute to motor preparation and planning during MI [34, 35]. Therefore, it is considered that activation of the central nervous system contributing to motor preparation and planning during MI is responsible for increased excitability of the spinal motor neurons via the descending pathways, such as the corticospinal and

strate significant differences between two MI conditions (**Table 8**).

*Comparison of relative values of the F-wave between 50% MI and 100% MI condition.*

*DOI: http://dx.doi.org/10.5772/intechopen.91834*

#### **Table 5.**

*Comparison of relative values of the F-wave among 10% MI, 30% MI, 50% MI, and 70% MI.*


#### **Table 6.**

*Somatosensory and Motor Research*

*The F-wave under 30% MI condition.*

*The F-wave under 50% MI condition.*

**78**

**Table 5.**

**Table 4.**

**Table 2.**

**Table 3.**

*The F-wave under 70% MI condition.*

*Comparison of relative values of the F-wave among 10% MI, 30% MI, 50% MI, and 70% MI.*

*The persistence and F/M amplitude ratio under 50% MI condition.*


#### **Table 7.**

*The persistence and F/M amplitude ratio under 100% MI condition.*

The relative values of the persistence and F/M amplitude ratio did not demonstrate significant differences between two MI conditions (**Table 8**).

## **2.7 Discussion**

Both persistence and the F/M amplitude ratio significantly increased during MI under all five MI conditions. Previous studies demonstrated that various brain regions, including the primary motor cortex, premotor area, supplementary motor area, prefrontal cortex, parietal lobule, cingulate area, cerebellum, and basal ganglia, contribute to motor preparation and planning during MI [34, 35]. Therefore, it is considered that activation of the central nervous system contributing to motor preparation and planning during MI is responsible for increased excitability of the spinal motor neurons via the descending pathways, such as the corticospinal and extrapyramidal tracts.


#### **Table 8.**

*Comparison of relative values of the F-wave between 50% MI and 100% MI condition.*

Furthermore, participants performed MI while holding the sensor of a pinch meter. Mizuguchi et al. [36] reported that while holding an object, the corticospinal excitability during MI was modulated by a combination of tactile and proprioceptive inputs. Thus, it is plausible that holding the pinch meter sensor during MI caused tactile and proprioceptive perceptions to cooperatively increase the excitability of the spinal motor neurons along the MI-activated pathways.

Relative values of persistence and the F/M amplitude were similar among all MI conditions. This result indicated that the magnitude of imagined muscle contraction strength may not affect the excitability of the spinal motor neurons. Bonnet et al. [37] reported that the H-reflex amplitude during MI was similar between 2 and 10% MI conditions. Hale et al. [38] also reported that the H-reflex amplitude during MI of ankle plantar flexion was similar among five (i.e., 20, 40, 60, 80, and 100% MVC) MI conditions. Similarly, Aoyama et al. [39] reported that the H-reflex amplitude during MI was similar between 50 and 100% MI conditions. MI is the mental representation of a movement in the absence of any overt movement [9]. The neural mechanism that inhibits actual movement and muscle contraction during MI may be involved in this outcome. Park et al. [40] reported that MEP amplitudes during MI were similar among all six (i.e., 10, 20, 30, 40, 50, and 60% MVC) MI conditions. Furthermore, magnitude of the primary motor cortex activity during MI did not correlate with the imagined muscle contraction strength, whereas activities of the supplementary motor and premotor areas during MI strongly correlated with it [41]. The supplementary motor and premotor areas have crucial roles in larger force generation [42], motor planning, preparation, and inhibition [43, 44]. Thus, these areas may inhibit actual muscle contractions depending on the magnitude of the muscle contraction strength. These areas are also connected directly to the primary motor cortex, and inhibitory inputs from them may suppress any additional primary motor cortex excitation conferred by MI with a high imagined contraction strength. Therefore, the degree of excitability of spinal motor neurons during MI at various imagined muscle contraction strengths may be modulated by both excitatory and inhibitory inputs from the central nervous system.

#### **2.8 Conclusion**

The result of these previous studies demonstrated that MI can increase the excitability of spinal motor neurons. Further, MI at slight imagined muscle contraction strength (i.e., 10% MVC) can substantially facilitate the excitability of spinal motor neurons.

## **3. The influence of duration of MI on the excitability of spinal motor neurons**

#### **3.1 Background and purpose**

In our previous studies, duration of MI was 1 min [23–26]. However, Driskell et al. [45] indicated that 10–15 min may be appropriate for duration of MI training session. Further, Twinning et al. [46] indicated that 5 min is the temporal limit to concentrate and perform MI. Therefore, we aimed to investigate the influence of duration of MI on the excitability of spinal motor neurons [25, 26, 47].

**81**

**Table 9.**

*The F-wave during MI for 5 min.*

*Motor Imagery for Neurorehabilitation: The F-Wave Study*

ducted in accordance with the Declaration of Helsinki.

recorded during relaxation for 1 min (post).

perform MI vividly) to 7 (very easy to perform MI vividly).

Eleven healthy adults participated (mean age = 26.4 ± 6.0 years). Written informed consent was obtained prior to participation. The study was approved by the Research Ethics Committee at Kansai University of Health Sciences and con-

Firstly, to determine the baseline of the excitability of spinal motor neurons, the F-wave was recorded during relaxation for 1 min (rest). Subsequently, participants were instructed to learn isometric left thenar muscle activity at 50% MVC for 1 min. For MI trial, participants imagined isometric left thenar muscle activity at 50% MVC for 1 min. The F-wave was recorded at 1, 3, and 5 min after beginning of MI (1-, 3-, and 5-min MI). Immediately after MI trial for 5 min, the F-wave was

After F-wave recording, participants evaluated their vividness of MI (i.e., how vividly they could imagine isometric thenar muscle activity at 50% MVC) at 1-, 3-, and 5-min MI using a seven-point Likert scale ranging from 1 (very difficult to

A nonparametric method was used for statistical analyses because the normality

Persistence at 1- and 3-min MI trial was significantly higher than rest (**Table 9**). No significant difference in persistence was observed between 5-min MI and rest trial (**Table 9**). Further, no significant differences in persistence were confirmed

of obtained data was not confirmed with the Shapiro-Wilk test. Persistence and the F/M amplitude ratio among five trials (rest, 1-, 3-, and 5-min MI, and post) were compared using the Friedman test and Scheffe's post hoc test. Rating scores of MI vividness at 1-, 3-, and 5-min MI were compared using the Friedman test and Scheffe's post hoc test. The threshold for statistical significance was set at *p* = 0.05.

*DOI: http://dx.doi.org/10.5772/intechopen.91834*

**3.2 Materials and methods**

*3.2.2 Experimental protocol*

**3.3 Statistical analysis**

among 1-, 3-, and 5-min MI trial.

**3.4 Results**

*3.2.1 Participants*

## **3.2 Materials and methods**

## *3.2.1 Participants*

*Somatosensory and Motor Research*

pathways.

central nervous system.

spinal motor neurons.

**3.1 Background and purpose**

**2.8 Conclusion**

**neurons**

Furthermore, participants performed MI while holding the sensor of a pinch meter. Mizuguchi et al. [36] reported that while holding an object, the corticospinal excitability during MI was modulated by a combination of tactile and proprioceptive inputs. Thus, it is plausible that holding the pinch meter sensor during MI caused tactile and proprioceptive perceptions to cooperatively increase the excitability of the spinal motor neurons along the MI-activated

Relative values of persistence and the F/M amplitude were similar among all MI conditions. This result indicated that the magnitude of imagined muscle contraction strength may not affect the excitability of the spinal motor neurons. Bonnet et al. [37] reported that the H-reflex amplitude during MI was similar between 2 and 10% MI conditions. Hale et al. [38] also reported that the H-reflex amplitude during MI of ankle plantar flexion was similar among five (i.e., 20, 40, 60, 80, and 100% MVC) MI conditions. Similarly, Aoyama et al. [39] reported that the H-reflex amplitude during MI was similar between 50 and 100% MI conditions. MI is the mental representation of a movement in the absence of any overt movement [9]. The neural mechanism that inhibits actual movement and muscle contraction during MI may be involved in this outcome. Park et al. [40] reported that MEP amplitudes during MI were similar among all six (i.e., 10, 20, 30, 40, 50, and 60% MVC) MI conditions. Furthermore, magnitude of the primary motor cortex activity during MI did not correlate with the imagined muscle contraction strength, whereas activities of the supplementary motor and premotor areas during MI strongly correlated with it [41]. The supplementary motor and premotor areas have crucial roles in larger force generation [42], motor planning, preparation, and inhibition [43, 44]. Thus, these areas may inhibit actual muscle contractions depending on the magnitude of the muscle contraction strength. These areas are also connected directly to the primary motor cortex, and inhibitory inputs from them may suppress any additional primary motor cortex excitation conferred by MI with a high imagined contraction strength. Therefore, the degree of excitability of spinal motor neurons during MI at various imagined muscle contraction strengths may be modulated by both excitatory and inhibitory inputs from the

The result of these previous studies demonstrated that MI can increase the excitability of spinal motor neurons. Further, MI at slight imagined muscle contraction strength (i.e., 10% MVC) can substantially facilitate the excitability of

**3. The influence of duration of MI on the excitability of spinal motor** 

In our previous studies, duration of MI was 1 min [23–26]. However, Driskell et al. [45] indicated that 10–15 min may be appropriate for duration of MI training session. Further, Twinning et al. [46] indicated that 5 min is the temporal limit to concentrate and perform MI. Therefore, we aimed to investigate the influence of

duration of MI on the excitability of spinal motor neurons [25, 26, 47].

**80**

Eleven healthy adults participated (mean age = 26.4 ± 6.0 years). Written informed consent was obtained prior to participation. The study was approved by the Research Ethics Committee at Kansai University of Health Sciences and conducted in accordance with the Declaration of Helsinki.

## *3.2.2 Experimental protocol*

Firstly, to determine the baseline of the excitability of spinal motor neurons, the F-wave was recorded during relaxation for 1 min (rest). Subsequently, participants were instructed to learn isometric left thenar muscle activity at 50% MVC for 1 min. For MI trial, participants imagined isometric left thenar muscle activity at 50% MVC for 1 min. The F-wave was recorded at 1, 3, and 5 min after beginning of MI (1-, 3-, and 5-min MI). Immediately after MI trial for 5 min, the F-wave was recorded during relaxation for 1 min (post).

After F-wave recording, participants evaluated their vividness of MI (i.e., how vividly they could imagine isometric thenar muscle activity at 50% MVC) at 1-, 3-, and 5-min MI using a seven-point Likert scale ranging from 1 (very difficult to perform MI vividly) to 7 (very easy to perform MI vividly).

## **3.3 Statistical analysis**

A nonparametric method was used for statistical analyses because the normality of obtained data was not confirmed with the Shapiro-Wilk test. Persistence and the F/M amplitude ratio among five trials (rest, 1-, 3-, and 5-min MI, and post) were compared using the Friedman test and Scheffe's post hoc test. Rating scores of MI vividness at 1-, 3-, and 5-min MI were compared using the Friedman test and Scheffe's post hoc test. The threshold for statistical significance was set at *p* = 0.05.

### **3.4 Results**

Persistence at 1- and 3-min MI trial was significantly higher than rest (**Table 9**). No significant difference in persistence was observed between 5-min MI and rest trial (**Table 9**). Further, no significant differences in persistence were confirmed among 1-, 3-, and 5-min MI trial.



#### **Table 10.**

*Rating scores of MI vividness during MI for 5 min.*

The F/M amplitude ratio at 1- and 3-min MI trial was significantly higher than rest (**Table 9**). The F/M amplitude ratio at 5-min MI trial was significantly smaller than 1- and 3-min MI trial (**Table 9**). Further, no significant difference in the F/M amplitude ratio was observed between 5-min MI and rest trial (**Table 9**).

The rating score of MI vividness at 5-min MI trial was significantly smaller that 1-min MI trial (**Table 10**).

#### **3.5 Discussion**

The results for the F-wave indicated that duration of MI for 1–3 min positively affects the excitability of spinal motor neurons. Further, the results of vividness of MI indicated that temporal limitation of MI, participants can perform MI vividly, may be 3 min.

It is considered that mental fatigue and/or habituation were involved in this result. Repetitive MI of a handgrip movement decreases the corticospinal excitability [48]. Rozand et al. [49] also demonstrated that participants felt difficulty to maintain their focus on imagined movement due to mental fatigue. Therefore, mental fatigue caused by sustained mental activity may affect the excitability of spinal motor neurons.

Brain activity was decreased by habituation after cognitive motor task for 10 min [50]. Further, the corticospinal excitability was also decreased by habituation [50]. At spinal level, the T-reflex amplitude was decreased after sustained mental activity for 20 min [51]. Therefore, habituation after sustained mental activity as MI can alter the corticospinal excitability, including the excitability of spinal motor neurons.

#### **3.6 Conclusion**

The result of this study demonstrated that longer duration of MI above 3 min has no facilitatory effect on the excitability of spinal motor neurons. Therefore, in physical therapy, the duration of MI should be considered.

## **4. The influence of imagery strategy on the excitability of spinal motor neurons**

#### **4.1 Background and purpose**

Previously, we investigated the influence of MI of isometric thenar muscle activity on the excitability of spinal motor neurons [18, 23–26]. Previous results indicated that the MI of thenar muscle activity at 50% MVC can increase the excitability of spinal motor neurons. However, there were individual differences in facilitation amount of the excitability of spinal motor neurons.

**83**

*Motor Imagery for Neurorehabilitation: The F-Wave Study*

ducted in accordance with the Declaration of Helsinki.

MI includes various components of perception that can be associated with actual movement [52]. Therefore, the effects of MI may differ depending on the choice of sensory modality. Then, we investigated that imagery strategy on the excitability of

Fourteen healthy adults (mean age = 23.4 ± 4.8 years) participated. Written informed consent was obtained prior to participation. The study was approved by the Research Ethics Committee at Kansai University of Health Sciences and con-

For the rest trial (rest), to determine the baseline excitability of the spinal motor

After the F-wave recording, participants evaluated difficulty of each imagery strategy by using a five-point Likert scale, ranging from 1 (very hard to image

A nonparametric method was used for statistical analyses because the normality of obtained data was not confirmed with the Shapiro-Wilk test. Persistence and the F/M amplitude ratio among four trials (rest, SI, KI, and SKI) were compared using the Friedman test and Scheffe's post hoc test. Rating scores of each imagery strategy (SI, KI, and SKI) were compared using the Friedman test and Scheffe's post hoc

test. The threshold for statistical significance was set at *p* = 0.05.

Persistence was significantly higher during SI and KI trials than at rest (**Table 11**). Persistence tended to be higher during SKI than at rest (**Table 11**). The F/M amplitude ratio was significantly higher during KI than at rest

The rating score of SKI vividness was significantly smaller than rest (**Table 12**).

Persistence and the F/M amplitude ratio were significantly increased during KI. Described in Introduction section, numerous studies demonstrated that various brain areas, including the primary motor cortex, were activated during KI [34, 35].

neurons, the F-wave was recorded during relaxation for 1 min. Subsequently, participants were instructed to exert isometric left thenar muscle contraction at 50% MVC for 1 min with visual feedback. Simultaneously, participants learned two imagery strategies: somatosensory (tactile and pressure perception of thumb finger pulp during pressing the sensor of pinch meter) and kinesthetic (thenar muscle contraction during pressing the sensor of pinch meter at 50% MVC). Subsequently, participants performed the somatosensory imagery (SI), kinesthetic imagery (KI), and combined somatosensory and kinesthetic imagery (SKI). In SKI trial, participants imagined somatosensory and kinesthetic sensation simultaneously. The

*DOI: http://dx.doi.org/10.5772/intechopen.91834*

spinal motor neurons [53].

**4.2 Materials and methods**

*4.2.2 Experimental protocol*

duration of each MI session was 1 min.

vividly) to 5 (very easy to image vividly).

**4.3 Statistical analysis**

**4.4 Results**

(**Table 11**).

**4.5 Discussion**

*4.2.1 Participants*

MI includes various components of perception that can be associated with actual movement [52]. Therefore, the effects of MI may differ depending on the choice of sensory modality. Then, we investigated that imagery strategy on the excitability of spinal motor neurons [53].

## **4.2 Materials and methods**

## *4.2.1 Participants*

*Somatosensory and Motor Research*

1-min MI trial (**Table 10**).

*Rating scores of MI vividness during MI for 5 min.*

**3.5 Discussion**

**Table 10.**

may be 3 min.

spinal motor neurons.

**3.6 Conclusion**

**neurons**

**4.1 Background and purpose**

The F/M amplitude ratio at 1- and 3-min MI trial was significantly higher than rest (**Table 9**). The F/M amplitude ratio at 5-min MI trial was significantly smaller than 1- and 3-min MI trial (**Table 9**). Further, no significant difference in the F/M

The rating score of MI vividness at 5-min MI trial was significantly smaller that

The results for the F-wave indicated that duration of MI for 1–3 min positively affects the excitability of spinal motor neurons. Further, the results of vividness of MI indicated that temporal limitation of MI, participants can perform MI vividly,

It is considered that mental fatigue and/or habituation were involved in this result. Repetitive MI of a handgrip movement decreases the corticospinal excitability [48]. Rozand et al. [49] also demonstrated that participants felt difficulty to maintain their focus on imagined movement due to mental fatigue. Therefore, mental fatigue caused by sustained mental activity may affect the excitability of

Brain activity was decreased by habituation after cognitive motor task for 10 min [50]. Further, the corticospinal excitability was also decreased by habituation [50]. At spinal level, the T-reflex amplitude was decreased after sustained mental activity for 20 min [51]. Therefore, habituation after sustained mental activity as MI can alter the

The result of this study demonstrated that longer duration of MI above 3 min has no facilitatory effect on the excitability of spinal motor neurons. Therefore, in

**4. The influence of imagery strategy on the excitability of spinal motor** 

Previously, we investigated the influence of MI of isometric thenar muscle activity on the excitability of spinal motor neurons [18, 23–26]. Previous results indicated that the MI of thenar muscle activity at 50% MVC can increase the excitability of spinal motor neurons. However, there were individual differences in facilitation

corticospinal excitability, including the excitability of spinal motor neurons.

physical therapy, the duration of MI should be considered.

amount of the excitability of spinal motor neurons.

amplitude ratio was observed between 5-min MI and rest trial (**Table 9**).

**82**

Fourteen healthy adults (mean age = 23.4 ± 4.8 years) participated. Written informed consent was obtained prior to participation. The study was approved by the Research Ethics Committee at Kansai University of Health Sciences and conducted in accordance with the Declaration of Helsinki.

## *4.2.2 Experimental protocol*

For the rest trial (rest), to determine the baseline excitability of the spinal motor neurons, the F-wave was recorded during relaxation for 1 min. Subsequently, participants were instructed to exert isometric left thenar muscle contraction at 50% MVC for 1 min with visual feedback. Simultaneously, participants learned two imagery strategies: somatosensory (tactile and pressure perception of thumb finger pulp during pressing the sensor of pinch meter) and kinesthetic (thenar muscle contraction during pressing the sensor of pinch meter at 50% MVC). Subsequently, participants performed the somatosensory imagery (SI), kinesthetic imagery (KI), and combined somatosensory and kinesthetic imagery (SKI). In SKI trial, participants imagined somatosensory and kinesthetic sensation simultaneously. The duration of each MI session was 1 min.

After the F-wave recording, participants evaluated difficulty of each imagery strategy by using a five-point Likert scale, ranging from 1 (very hard to image vividly) to 5 (very easy to image vividly).

## **4.3 Statistical analysis**

A nonparametric method was used for statistical analyses because the normality of obtained data was not confirmed with the Shapiro-Wilk test. Persistence and the F/M amplitude ratio among four trials (rest, SI, KI, and SKI) were compared using the Friedman test and Scheffe's post hoc test. Rating scores of each imagery strategy (SI, KI, and SKI) were compared using the Friedman test and Scheffe's post hoc test. The threshold for statistical significance was set at *p* = 0.05.

### **4.4 Results**

Persistence was significantly higher during SI and KI trials than at rest (**Table 11**). Persistence tended to be higher during SKI than at rest (**Table 11**).

The F/M amplitude ratio was significantly higher during KI than at rest (**Table 11**).

The rating score of SKI vividness was significantly smaller than rest (**Table 12**).

## **4.5 Discussion**

Persistence and the F/M amplitude ratio were significantly increased during KI. Described in Introduction section, numerous studies demonstrated that various brain areas, including the primary motor cortex, were activated during KI [34, 35].


#### **Table 11.**

*The F-wave during SI, KI, and SKI, trail.*


#### **Table 12.**

*Rating scores of MI vividness during SI, KI, and SKI, trail.*

The corticospinal excitability was significantly increased during KI [2, 15]. Therefore, the excitability of spinal motor neurons during KI may be increased via the descending pathways, such as the corticospinal and extrapyramidal tracts.

Although there was no significant difference in the F/M amplitude ratio between SI and rest trial, persistence was significantly increased during SI than rest. We did not expect this result previously, because there are no previous studies reported that SI increases the corticospinal excitability including that of the primary motor cortex. One possible is that SI adopted in this study included kinesthetic components. Participants in this study imagined tactile and pressure perception accompanied with holding the sensor of a pinch meter. Therefore, it is plausible that participants imagined tactile and perception along with thenar muscle activity.

Persistence during SKI was tended to be higher than rest, and the rating score of SKI vividness was the lowest among all imagery strategies (SI, KI, and SKI). Participants in this study were instructed to pay attention to kinesthetic and somatosensory perception simultaneously. The decline in the amount of attention that can be allocated to each imagery strategy may have increased difficulty for participants to perform SKI vividly. Indeed, Williams et al. [54] indicated that there are positive correlation between the corticospinal excitability and MI vividness.

#### **4.6 Conclusion**

The result of this study indicated that KI may have a greater effect on the excitability of spinal motor neurons.

### **5. How to use MI in neurorehabilitation**

In post-stroke and spinal cord injury, motor cortex excitability was decreased due to damage of neural substrates, loss of sensory inputs, and disuse of affected

**85**

**Author details**

may be less than 3 min.

**Conflict of interest**

Yoshibumi Bunno

Health Sciences, Osaka, Japan

\*Address all correspondence to: bunno@kansai.ac.jp

provided the original work is properly cited.

The authors declare no conflict of interest.

Graduate School of Health Sciences, Graduate School of Kansai University of

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

*Motor Imagery for Neurorehabilitation: The F-Wave Study*

limb [1]. Further, the MEP amplitude was decreased after stroke [55] and spinal cord injury [56]. Additionally, a significant reduction of spinal motor neuron excitability has been shown in the post-stroke acute phase [4] and spinal cord injury [57]. Facilitating the corticospinal excitability is closely related to functional motor recovery [58]. Therefore, the immediate enrollment in rehabilitation programs aiming to facilitate the corticospinal excitability, including the excitability of spinal motor neurons, should be important. Our previous researches investigated the excitability of spinal motor neurons during MI in only healthy volunteers. However, Cicinelli et al. [59] reported that the MEP amplitude was significantly facilitated during MI in post-stroke. Naseri et al. [60] reported that the amplitude and persistence of the F-wave were significantly increased during MI in post-stroke. Further, similar effect was observed in spinal cord injury [61]. Also, in Parkinson's disease, the amplitude and persistence of the F-wave were significantly increased during MI [62]. Therefore, MI has a facilitating effect on the corticospinal excitability, including the excitability of spinal motor neurons,

Next, about definite method of MI, our research group revealed that MI of isometric thenar muscle activity at 50% MVC can increase the excitability of spinal motor neurons. Additionally, imagined muscle contraction strength did not affect facilitation amount of the excitability of spinal motor neurons. In physical therapy for facilitating the excitability of spinal motor neurons, slight (i.e., 10% MVC) imagined muscle contraction strength may be sufficient. Then, kinesthetic imagery could more facilitate the excitability of spinal motor neurons than somatosensory imagery. Stinear et al. [63] reported that kinesthetic imagery can significantly increase the corticospinal excitability. Therefore, to facilitate the excitability of spinal motor neurons, kinesthetic perception may be used for imagery strategy. Also considering mental fatigue and habituation, duration of MI

*DOI: http://dx.doi.org/10.5772/intechopen.91834*

for central nervous system disorder.

*Motor Imagery for Neurorehabilitation: The F-Wave Study DOI: http://dx.doi.org/10.5772/intechopen.91834*

*Somatosensory and Motor Research*

*The F-wave during SI, KI, and SKI, trail.*

**Table 11.**

**Table 12.**

The corticospinal excitability was significantly increased during KI [2, 15]. Therefore, the excitability of spinal motor neurons during KI may be increased via the descend-

Although there was no significant difference in the F/M amplitude ratio between SI and rest trial, persistence was significantly increased during SI than rest. We did not expect this result previously, because there are no previous studies reported that SI increases the corticospinal excitability including that of the primary motor cortex. One possible is that SI adopted in this study included kinesthetic components. Participants in this study imagined tactile and pressure perception accompanied with holding the sensor of a pinch meter. Therefore, it is plausible that participants

Persistence during SKI was tended to be higher than rest, and the rating score of SKI vividness was the lowest among all imagery strategies (SI, KI, and SKI). Participants in this study were instructed to pay attention to kinesthetic and somatosensory perception simultaneously. The decline in the amount of attention that can be allocated to each imagery strategy may have increased difficulty for participants to perform SKI vividly. Indeed, Williams et al. [54] indicated that there are positive correlation between the corticospinal excitability and MI vividness.

The result of this study indicated that KI may have a greater effect on the

In post-stroke and spinal cord injury, motor cortex excitability was decreased due to damage of neural substrates, loss of sensory inputs, and disuse of affected

ing pathways, such as the corticospinal and extrapyramidal tracts.

*Rating scores of MI vividness during SI, KI, and SKI, trail.*

imagined tactile and perception along with thenar muscle activity.

**84**

**4.6 Conclusion**

excitability of spinal motor neurons.

**5. How to use MI in neurorehabilitation**

limb [1]. Further, the MEP amplitude was decreased after stroke [55] and spinal cord injury [56]. Additionally, a significant reduction of spinal motor neuron excitability has been shown in the post-stroke acute phase [4] and spinal cord injury [57]. Facilitating the corticospinal excitability is closely related to functional motor recovery [58]. Therefore, the immediate enrollment in rehabilitation programs aiming to facilitate the corticospinal excitability, including the excitability of spinal motor neurons, should be important. Our previous researches investigated the excitability of spinal motor neurons during MI in only healthy volunteers. However, Cicinelli et al. [59] reported that the MEP amplitude was significantly facilitated during MI in post-stroke. Naseri et al. [60] reported that the amplitude and persistence of the F-wave were significantly increased during MI in post-stroke. Further, similar effect was observed in spinal cord injury [61]. Also, in Parkinson's disease, the amplitude and persistence of the F-wave were significantly increased during MI [62]. Therefore, MI has a facilitating effect on the corticospinal excitability, including the excitability of spinal motor neurons, for central nervous system disorder.

Next, about definite method of MI, our research group revealed that MI of isometric thenar muscle activity at 50% MVC can increase the excitability of spinal motor neurons. Additionally, imagined muscle contraction strength did not affect facilitation amount of the excitability of spinal motor neurons. In physical therapy for facilitating the excitability of spinal motor neurons, slight (i.e., 10% MVC) imagined muscle contraction strength may be sufficient. Then, kinesthetic imagery could more facilitate the excitability of spinal motor neurons than somatosensory imagery. Stinear et al. [63] reported that kinesthetic imagery can significantly increase the corticospinal excitability. Therefore, to facilitate the excitability of spinal motor neurons, kinesthetic perception may be used for imagery strategy. Also considering mental fatigue and habituation, duration of MI may be less than 3 min.

### **Conflict of interest**

The authors declare no conflict of interest.

## **Author details**

Yoshibumi Bunno Graduate School of Health Sciences, Graduate School of Kansai University of Health Sciences, Osaka, Japan

\*Address all correspondence to: bunno@kansai.ac.jp

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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**91**

**Chapter 6**

from LF/HF

*Yuki Fukumoto*

motor accuracy, pinch task

**1. Introduction**

**Abstract**

Effective Motor Imagery

Application: Examining Spinal

Cord Excitability from the F-Wave

Motor imagery can be helpful for the therapeutic approach for the patients who have difficulty in the actual motion. This chapter explains the following important six points for getting high-effective motor imagery based on the neuroscience. First, excitability of spinal motor neuron was increased by motor imagery. However, adding effect on breathing state, both expiration and inspiration phase on the relax respiration, does not influence the excitability of spinal motor neuron. Also, motor imagery increased the excitability of spinal motor neuron and cardiac sympathetic nerve activity. However, vividness of motor imagery was to converge a degree. Motor practice before motor imagery was important. Motor practice was appropriate for 30 s using intermittent visual feedback, and for doing motor imagery, time enough was 1 min. Adding motor imagery method was a recommended composite for kinesthetic and visual motor imagery. Unfortunately, motor imagery has few effects for the other hand. Therefore, motor imagery should be done on the ipsilateral side from the previous motor practice.

**Keywords:** motor imagery, motor practice, F-wave, LF/HF, breathing state,

The aim of rehabilitation is to improve motor function. Physical therapists distinguish physical limitations and do therapy for patients. The other effective method was doing self-training for the patient oneself [1]. However, self-training may be carefulness or contraindication when it merges heart trouble and respiratory illness. Therefore, we think necessarily self-training without actual motion, and we suggest motor imagery on self-training. Motor imagery especially involves the activation of cognitive processes from working memory [2]. Motor imagery is not limitation time, place, and using special equipment. Combination therapy for actual motion and motor imagery was improvement of upper limb function than only actual motion in post-stroke hemiparesis patients [3]. The only motor imagery case [4] is the comparison of muscular strengths after motor imagery of the little finger maximum voluntary contraction (MVC) abduction movement for 4 weeks

and Autonomic Nervous Activity

## **Chapter 6**

*Somatosensory and Motor Research*

cercor/bhi103

Imagery-induced cortical excitability changes in stroke: A transcranial magnetic stimulation study. Cerebral Cortex. 2006;**16**:247-253. DOI: 10.1093/

[60] Naseri M, Petramfar P, Ashraf A. Effect of motor imagery on the F-wave parameters in hemiparetic stroke survivors. Annals of Rehabilitation Medicine. 2015;**39**:401-408. DOI:

[61] Cramer SC, Orr EL, Cohen MJ, Lacourse MG. Effects of motor imagery

training after chronic, complete spinal cord injury. Experimental Brain Research. 2007;**177**:33-242. DOI:

[62] Suzuki T, Bunno Y, Onigata C, Tani M, Uragami S, Yoshida S. Excitability of spinal neural function during motor imagery in Parkinson's disease. Functional Neurology. 2014;**29**:

10.1007/s00221-006-0662-9

[63] Stinear CM, Byblow WD, Steyvers M, Levin O, Swinnen SP. Kinesthetic, but not visual, motor imagery modulates corticomotor excitability. Experimental Brain Research. 2006;**168**:157-164. DOI: 10.1007/s00221-005-0078-y

263-267

10.5535/arm.2015.39.3.401

**90**
