**4. How to detect and record tremor?**

There are several ways for measuring human tremor. However, even today, the most used methods are those that makes the use of severity scales [17; 18]. In these methods, the patients are asked to perform different drawing patterns such as spirals, circles and letters (Figures 1 to 9). These drawings are subsequently classified by neurologists according to a numeric scale, usually ranging from 0 (no visible tremor) to 5 (severe disabling tremor). The drawings made by patients are then compared with examples of previous researches, carried out taking into account others patients previously classified. Therefore, this type of classification consists in a visual comparison and contains the subjectivity of the expert responsible for the analysis. In addition, this analysis prevents the extraction of critical information from tremor activity, such as frequency, amplitude and speed.

Human Tremor: Origins, Detection and Quantification 9

**Figure 2.** Action tremor. Male patient born in 1934. Date: 09/03/2009.

**Figure 3.** Action tremor. Male patient born in 1934 after treatment with levodopa. Date: 10/05/2010.

**Figure 1.** Action tremor. Male patient born in 1934. Date: 09/03/2009.

Human Tremor: Origins, Detection and Quantification 9

**Figure 2.** Action tremor. Male patient born in 1934. Date: 09/03/2009.

**4. How to detect and record tremor?** 

There are several ways for measuring human tremor. However, even today, the most used methods are those that makes the use of severity scales [17; 18]. In these methods, the patients are asked to perform different drawing patterns such as spirals, circles and letters (Figures 1 to 9). These drawings are subsequently classified by neurologists according to a numeric scale, usually ranging from 0 (no visible tremor) to 5 (severe disabling tremor). The drawings made by patients are then compared with examples of previous researches, carried out taking into account others patients previously classified. Therefore, this type of classification consists in a visual comparison and contains the subjectivity of the expert responsible for the analysis. In addition, this analysis prevents the extraction of critical

information from tremor activity, such as frequency, amplitude and speed.

**Figure 1.** Action tremor. Male patient born in 1934. Date: 09/03/2009.

**Figure 3.** Action tremor. Male patient born in 1934 after treatment with levodopa. Date: 10/05/2010.

Human Tremor: Origins, Detection and Quantification 11

**Figure 6.** Male patient born in 1937. Vascular tremor: left hand tremor since 1989, dizziness, hypertension, patellar hyperreflexia, leucoaraiose, brain volume reduction, brain gap and

**Figure 7.** Female patient born in 1983. Hand tremor for four years that gets worse with anxiety and while handling objects. Absence of neurological signs. Normal dosage of calcium and parathyroid

microangiopathy. Date: 05/08/2010.

hormone. Absence of familiar cases.

**Figure 4.** Action tremor. Male patient born in 1934 after treatment with levodopa. Date: 10/05/2010.

**Figure 5.** Male patient born in 1937. Vascular tremor: left hand tremor since 1989, dizziness, hypertension, patellar hyperreflexia, leucoaraiose, brain volume reduction, brain gap and microangiopathy. Date: 05/08/2010.

**Figure 4.** Action tremor. Male patient born in 1934 after treatment with levodopa. Date: 10/05/2010.

**Figure 5.** Male patient born in 1937. Vascular tremor: left hand tremor since 1989, dizziness, hypertension, patellar hyperreflexia, leucoaraiose, brain volume reduction, brain gap and

microangiopathy. Date: 05/08/2010.

**Figure 6.** Male patient born in 1937. Vascular tremor: left hand tremor since 1989, dizziness, hypertension, patellar hyperreflexia, leucoaraiose, brain volume reduction, brain gap and microangiopathy. Date: 05/08/2010.

**Figure 7.** Female patient born in 1983. Hand tremor for four years that gets worse with anxiety and while handling objects. Absence of neurological signs. Normal dosage of calcium and parathyroid hormone. Absence of familiar cases.

Human Tremor: Origins, Detection and Quantification 13

**Figure 9.** Female patient born in 1929. Left hand tremor, oblivion, normal neurological examination. Nuclear magnetic resonance of the brain: ischemic lacunar lesions, acute semioval center ischemia,

For the clinical diagnosis of tremor, it is necessary a complete and detailed medical history relative to factors, such as age of onset of tremor, family history, circumstances that modifies the tremor, use of drugs that can trigger the movement, existence of comorbidities, use of alcohol, smoking, anxiety, stress and depression. Besides this, it is important to do a clinical neurological exam analyzing the semiological aspects, with special focus on the type of tremor and how it presents, examining the patient standing, sitting, walking or performing movements of limbs (evidence of coordination of upper and lower limbs), supination and

Regarding to physiological and essential tremor, there is no need for further investigation. Laboratory tests are important to rule out endocrine (thyroid) or other extrapyramidal

slight brain reduction.

pronation movements, presence or absence of cog.

**Figure 8.** Female patient born in 1983. Hand tremor for four years that gets worse with anxiety and while handling objects. Absence of neurological signs. Normal dosage of calcium and parathyroid hormone. Absence of familiar cases.

**Figure 8.** Female patient born in 1983. Hand tremor for four years that gets worse with anxiety and while handling objects. Absence of neurological signs. Normal dosage of calcium and parathyroid

hormone. Absence of familiar cases.

**Figure 9.** Female patient born in 1929. Left hand tremor, oblivion, normal neurological examination. Nuclear magnetic resonance of the brain: ischemic lacunar lesions, acute semioval center ischemia, slight brain reduction.

For the clinical diagnosis of tremor, it is necessary a complete and detailed medical history relative to factors, such as age of onset of tremor, family history, circumstances that modifies the tremor, use of drugs that can trigger the movement, existence of comorbidities, use of alcohol, smoking, anxiety, stress and depression. Besides this, it is important to do a clinical neurological exam analyzing the semiological aspects, with special focus on the type of tremor and how it presents, examining the patient standing, sitting, walking or performing movements of limbs (evidence of coordination of upper and lower limbs), supination and pronation movements, presence or absence of cog.

Regarding to physiological and essential tremor, there is no need for further investigation. Laboratory tests are important to rule out endocrine (thyroid) or other extrapyramidal

diseases that manifest tremor, e.g. dosage of ceruloplasmin and copper, as well as eye examination (in Wilson's disease). Imaging and functional neuroimagins – PET and SPECT-CT positron and photon emission tomography may be useful in differentiation between essential and parkinsonian tremors, using markers for dopamine transporter or striatal dopaminergic terminals.

Human Tremor: Origins, Detection and Quantification 15

*Hoehn and Yahr Scale* – This tool is used in the evaluation of patients with Parkinson's disease, classifying them into six stages, ranging between 0 and 5 [3]. In its original version, this scale comprises five stages of evaluating the severity of Parkinson's disease and covers comprehensive measures of signs and symptoms, including postural instability, rigidity, tremor and bradiscinesia [24]. Patients classified between stages I and III have light to moderate stage of the disease, as those who fall between stages IV and V have severe disabilities, and the stage V indicates an inability to move alone. A modified version of Hoehn and Yahr Scale also features two intermediate stages for evaluation of disease [24]. The protocol of this tool includes tests that evaluate the severity of resting, postural and kinetic tremors. Besides this, the test includes tasks such as extension of the arms, ingestion of liquids using spoons and cups, drawings of the spiral of Archimedes and exercises like touch the own nose with the finger. The protocol also includes specific instructions for

*Washington Heights-Inwood Genetic Study of Essential Tremor (WHIGET)* – It is the most used tool in clinical assessment of essential tremor. This tool has emerged from a study started in 1955, which aimed to investigate genetic aspects of essential tremor by using methods not

*Bain* – Clinical examination of Bain consists in performing a series of tests that analyze the various components of tremor (resting tremor, postural tremor, kinetic tremor, intention tremor) [25]. The various components of the tremor are analyzed as follows: 1 - the resting component of the tremor of the head is measured with the patient lying on a couch with his head resting on cushions and postural component is collected with the patient sitting unsupported on the head and looking forward; 2 - component of the postural tremor of lower limbs is analyzed with the patient seated and with the extended leg, while the rest tremor is analyzed with the feet of the patient placed on the floor, the upper limbs are evaluated with the patient seated, three component of the tremor at rest is analyzed while the arms are relaxed and flat on the neck of the patient, while the postural component is analyzed with arms outstretched, hands pronated and fingers separated; 4 - the kinetic component is measured during the transitional phase of the test finger-nose and intentional component is measured while the finger of the subject gets closer to a target placed at reach. Vocal tremor is analyzed from the speech of each patient (patients should speak his own name, address and birthday) and, moreover, from the sound of singing from the patient, holding a musical note with the voice. All the tasks are scored from 0 to 10, as follows: 0-3 -

We can observe that clinical evaluation is not able to provide many answers regarding the evolution of the disease, since it does not consider the peculiarities of each patient and uses

Aiming to eliminate the subjectivity and limitations of the analysis methods based on scales some techniques to measure and analyse the tremor electronically have been developed. Thus, besides the methods employed in the clinical evaluation, many others are applied to evaluate the tremor in the laboratory. The most common methods are accelerometry,

the subjectivity of experts during the evaluation and classification of the individuals.

scoring and that the expert can classify each task performed by the patient.

light, 4-6 - moderate, 7-9 - severe and 10 - very severe [25].

yet implemented [3].

The different forms of assessment of tremor can be divided into clinical and biomechanical evaluation that takes into account qualitative and quantitative analysis. Clinical evaluation is based on clinical studies dedicated to the understanding of the characteristics, evolution and treatment of diseases, which has tremor as one of its manifestations. Thus, these evaluations are basically composed of scales. Currently, rating scales such as Washington Heights-Inwood Genetic Study of Essential Tremor – WHIGET tremor rating scale – wTRS [19; 20], Fahn-Tolosa-Marin Tremor Rating Scale [21], and the Essential Tremor Rating Assessment Scale – TETRAS [22] are used to evaluate essential tremor during the clinical examination. Each tremor rating scale subjectively scale the intensity of tremor from 0 to 4, generally corresponding (0) normal (1) slightly abnormal, (2) mildly abnormal (3), moderately abnormal, and (4) severely abnormal. Other scales are also used for evaluation of Parkinson's disease, such as UPDRS and Hoehn and Yahr. The UPDRS is a clinical tool for evaluating patients with this disorder. Recently, the Movement Disorder Society – MDS recommended a review, published in 2008, named MDS-UPDRS [16]. The MDS-UPDRS scale consists of a list of questions divided into four parts, in which the values 0-4 should be assigned depending on the severity of tremor: 0 - normal or smooth, 1 - minimum problems, 2 - mild impairment, 3 - moderate problems and 4 - serious problems. Another scale used to assess the level of Parkinson's diseases in patients is the Hoehn and Yahr. The scale is a simple staging that evaluates the overall severity of Parkinsonism based on bilateral motor dysfunction, involvement and the compromise of gait and balance. The original 5-point scale (Stage 1-5) was subsequently modified to a 7-point scale stages that included 1.5 and 2.5 in the 1990s [23].

The clinical evaluation of patients with pathological tremor is usually based on patterns that are obtained by observing groups of analysis. For each disease there is a standard for evaluation of patients. Some of these patterns are briefly described below.

*MDS-sponsored UPDRS Revision (MDS-UPDRS)* – Result of changes in the original pattern known as the Unified Parkinson's Disease Rating Scale (UPDRS), is the most used method for analyzing the development of Parkinson's disease. This tool is used for quantitative assessment and treatment of patients and consists in a list of questions divided into four parts, to which must be assigned values between 0 and 4, depending on the severity of the problem: 0 - normal, 1 - light, 2-soft, 3 - moderate, and 4 - severe. The MDS-UPDRS maintains the structure of the UPDRS, i.e contains four parts. However, these component parts have been modified in order to promote integration with elements of non-motor Parkinson's disease: part I - non-motor experiences of daily living; Part II - motor daily experiences, part III - motor examination, part IV - motor complications. Parts I and II are evaluated according to the patient's own responses to a questionnaire. The tool analyzes the symptoms of Parkinson's disease through clinical evaluation and patient self-report[24].

*Hoehn and Yahr Scale* – This tool is used in the evaluation of patients with Parkinson's disease, classifying them into six stages, ranging between 0 and 5 [3]. In its original version, this scale comprises five stages of evaluating the severity of Parkinson's disease and covers comprehensive measures of signs and symptoms, including postural instability, rigidity, tremor and bradiscinesia [24]. Patients classified between stages I and III have light to moderate stage of the disease, as those who fall between stages IV and V have severe disabilities, and the stage V indicates an inability to move alone. A modified version of Hoehn and Yahr Scale also features two intermediate stages for evaluation of disease [24]. The protocol of this tool includes tests that evaluate the severity of resting, postural and kinetic tremors. Besides this, the test includes tasks such as extension of the arms, ingestion of liquids using spoons and cups, drawings of the spiral of Archimedes and exercises like touch the own nose with the finger. The protocol also includes specific instructions for scoring and that the expert can classify each task performed by the patient.

14 Practical Applications in Biomedical Engineering

dopaminergic terminals.

2.5 in the 1990s [23].

diseases that manifest tremor, e.g. dosage of ceruloplasmin and copper, as well as eye examination (in Wilson's disease). Imaging and functional neuroimagins – PET and SPECT-CT positron and photon emission tomography may be useful in differentiation between essential and parkinsonian tremors, using markers for dopamine transporter or striatal

The different forms of assessment of tremor can be divided into clinical and biomechanical evaluation that takes into account qualitative and quantitative analysis. Clinical evaluation is based on clinical studies dedicated to the understanding of the characteristics, evolution and treatment of diseases, which has tremor as one of its manifestations. Thus, these evaluations are basically composed of scales. Currently, rating scales such as Washington Heights-Inwood Genetic Study of Essential Tremor – WHIGET tremor rating scale – wTRS [19; 20], Fahn-Tolosa-Marin Tremor Rating Scale [21], and the Essential Tremor Rating Assessment Scale – TETRAS [22] are used to evaluate essential tremor during the clinical examination. Each tremor rating scale subjectively scale the intensity of tremor from 0 to 4, generally corresponding (0) normal (1) slightly abnormal, (2) mildly abnormal (3), moderately abnormal, and (4) severely abnormal. Other scales are also used for evaluation of Parkinson's disease, such as UPDRS and Hoehn and Yahr. The UPDRS is a clinical tool for evaluating patients with this disorder. Recently, the Movement Disorder Society – MDS recommended a review, published in 2008, named MDS-UPDRS [16]. The MDS-UPDRS scale consists of a list of questions divided into four parts, in which the values 0-4 should be assigned depending on the severity of tremor: 0 - normal or smooth, 1 - minimum problems, 2 - mild impairment, 3 - moderate problems and 4 - serious problems. Another scale used to assess the level of Parkinson's diseases in patients is the Hoehn and Yahr. The scale is a simple staging that evaluates the overall severity of Parkinsonism based on bilateral motor dysfunction, involvement and the compromise of gait and balance. The original 5-point scale (Stage 1-5) was subsequently modified to a 7-point scale stages that included 1.5 and

The clinical evaluation of patients with pathological tremor is usually based on patterns that are obtained by observing groups of analysis. For each disease there is a standard for

*MDS-sponsored UPDRS Revision (MDS-UPDRS)* – Result of changes in the original pattern known as the Unified Parkinson's Disease Rating Scale (UPDRS), is the most used method for analyzing the development of Parkinson's disease. This tool is used for quantitative assessment and treatment of patients and consists in a list of questions divided into four parts, to which must be assigned values between 0 and 4, depending on the severity of the problem: 0 - normal, 1 - light, 2-soft, 3 - moderate, and 4 - severe. The MDS-UPDRS maintains the structure of the UPDRS, i.e contains four parts. However, these component parts have been modified in order to promote integration with elements of non-motor Parkinson's disease: part I - non-motor experiences of daily living; Part II - motor daily experiences, part III - motor examination, part IV - motor complications. Parts I and II are evaluated according to the patient's own responses to a questionnaire. The tool analyzes the symptoms of Parkinson's disease through clinical evaluation and patient self-report[24].

evaluation of patients. Some of these patterns are briefly described below.

*Washington Heights-Inwood Genetic Study of Essential Tremor (WHIGET)* – It is the most used tool in clinical assessment of essential tremor. This tool has emerged from a study started in 1955, which aimed to investigate genetic aspects of essential tremor by using methods not yet implemented [3].

*Bain* – Clinical examination of Bain consists in performing a series of tests that analyze the various components of tremor (resting tremor, postural tremor, kinetic tremor, intention tremor) [25]. The various components of the tremor are analyzed as follows: 1 - the resting component of the tremor of the head is measured with the patient lying on a couch with his head resting on cushions and postural component is collected with the patient sitting unsupported on the head and looking forward; 2 - component of the postural tremor of lower limbs is analyzed with the patient seated and with the extended leg, while the rest tremor is analyzed with the feet of the patient placed on the floor, the upper limbs are evaluated with the patient seated, three component of the tremor at rest is analyzed while the arms are relaxed and flat on the neck of the patient, while the postural component is analyzed with arms outstretched, hands pronated and fingers separated; 4 - the kinetic component is measured during the transitional phase of the test finger-nose and intentional component is measured while the finger of the subject gets closer to a target placed at reach. Vocal tremor is analyzed from the speech of each patient (patients should speak his own name, address and birthday) and, moreover, from the sound of singing from the patient, holding a musical note with the voice. All the tasks are scored from 0 to 10, as follows: 0-3 light, 4-6 - moderate, 7-9 - severe and 10 - very severe [25].

We can observe that clinical evaluation is not able to provide many answers regarding the evolution of the disease, since it does not consider the peculiarities of each patient and uses the subjectivity of experts during the evaluation and classification of the individuals.

Aiming to eliminate the subjectivity and limitations of the analysis methods based on scales some techniques to measure and analyse the tremor electronically have been developed. Thus, besides the methods employed in the clinical evaluation, many others are applied to evaluate the tremor in the laboratory. The most common methods are accelerometry,

electromyography (EMG) and spirography [5]. The biomechanical analysis of the tremor involves qualitative and quantitative aspects, and its main methods of measuring are electromyography (EMG), magnetic tracker system, active optical markers, accelerometers, gyroscopes and spirography.

Human Tremor: Origins, Detection and Quantification 17

Currently, there are devices for movement capture with wireless technology, that are capable to integrate accelerometers and gyroscopes. These devices are light and easy to use,

Furthermore, there are still new devices for tremor evaluation through videos [30] and tools that use accelerometers and transmit information through internet and Bluetooth technology [41]. The magnetic tracker system provides the movement displacement (x, y and z) and orientation (pitch, roll and yaw) of each body segment relative to a fixed transmitter [42]. From the active optical markers can be extracted the acceleration and the application of trigonometry makes possible the description of the vector orientation and the

Tremor quantification can be used to control the administration of therapeutic drugs [39]

The signal processing and analysis of tremor often involves the spectral analysis, based on Fast Fourier Transform – FFT [35; 39; 41], but this technique as modified weighted Fourier Linear Combiner –WFLC [44] is suitable for periodic or quasi-periodic estimation of motion with single dominant frequency, whereas Band-Limited Multiple Fourier Linear Combiner – BMFLC [34] is suitable for estimation of band limited signals consisting of multiple frequency components. Other methods can also be found as Detrended Fluctuation Analysis (DFA) to analyze hand essential tremor time-series extracted from regions around the first three main frequency components of the tremor power spectra – PWS [45]. To increase the accuracy other modifications or algorithms are used [46; 47]. However, it is not possible to determine the best way to perform these analyses, since this depends on the objectives of the study. Therefore, it is not possible to reach any conclusion on the most appropriate

Hand-drawing patterns are commonly assessed by means of visual rating scales.[48; 49] However, such scales provide only crude subjective estimates of tremor amplitude. In order to reduce the subjectivity and limitation of some methods based on visual scales, there have been developed a few strategies for electronically measuring tremor, such as accelerometry and digitizing tablets. The use of digitizing tablets is common and provides the possibility

The usual function of a digitizing tablet is to enable the analysis of drawings directly on the computer. The measurement of tremor by using digitizing tablets is a non-invasive alternative for tremor detection that combines simplicity with the precision and versatility of computational methods. The digitizing tablet is able to inform the position of the tip of the pen on its surface. By using this property this device can detect the movement of a subject

Subjectively interpreted in previous decades, nowadays the digital spirography can provide quantitative data of the movement control [57]. The spirography has been considered valid and reliable to diagnose early Parkinson's disease [58], essential tremor [59] and to distinguish tremulous parkinsonian patients with normal presynaptic dopaminergic

following standard drawing patterns placed on it [27; 49; 50; 51; 52; 53; 54; 55; 56]

being commonly used for the study of tremor [39].

and the optimization of deep brain stimulation [40].

methodologies for the detection and diagnosis of tremor [3].

of tremor activity detection under kinetic conditions.

estimation of limb posture [43].

The most common method for eletronic evaluation of tremor is the accelerometry, which makes use of sensors to measure the acceleration of a body part [12; 26; 27; 28]. Accelerometers are the main tool for the identification of tremor, easily observed by the large number of recent studies addressing the assessment of tremor [29; 30; 31; 32; 33; 34; 35]. The accelerometers measure linear acceleration forces in three orthogonal directions, being able to capture the movement of members produced by the action of gravity and muscle action, including tremors.

In accelerometry, data acquisition is performed by a sensor known as accelerometer that based on the Newton's second law, is capable of measuring the acceleration of a body. The accelerometer consists of an electromechanical device, usually based on the piezoelectric effect or the variation of capacitance which, when attached to any part of the body is capable of measuring acceleration forces or the movement caused by the tremor. This device generates a sequence of values (time-series) representing the instantaneous value of the acceleration as a function of time on the body part in which the sensor has been set. This series is stored and it can later be analyzed computationally.

Following this same logic (electronic evaluation, storage and computational analysis), other methods have been proposed, such as gyroscopes (evaluation of angular displacement) and speed / position transducers of many types [11; 29].

Gyroscopes are devices used to measure angular velocity. It is a simple device to detect the rate of change in the orientation of each segment and are insensitive to gravitational force [36].

Another tool to detect tremor consists in the use of electromyography. The electromyographic signal (EMG) can be considered as the superposition of individual activity of several active motor units during muscle contraction and may be used to diagnose many types of neuromuscular disorders. The EMG signal may be picked up by electrodes placed on the skin surface or by means of needle / wire electrodes which are introduced into the muscle tissue [26; 27; 28; 37].

Electromyography is an experimental technique concerned with the development, recording and analysis of myoelectric signals. The frequency (Hz), mean amplitude (mV) and pattern (synchronous or alternating) are used to evaluate the tremor [38].

In the acquisition of electromyographic signals for tremor analysis is common to use a specific task with the use of weights to reduce the influence of the heartbeat on the acquired electromyographic signal. For example, Elble (2003) compared the tremor in two groups of healthy individuals, a group of young (20-42 years old) and another group of elderly (70-92 years old). Elble analyzed the signals obtained in a state without load and with the addition of a weight of 300g. In this study, subjects were seated with the forearm supported and hands at rest or under load (palm and fingers extended in a straight line with the forearm).

Currently, there are devices for movement capture with wireless technology, that are capable to integrate accelerometers and gyroscopes. These devices are light and easy to use, being commonly used for the study of tremor [39].

16 Practical Applications in Biomedical Engineering

gyroscopes and spirography.

muscle action, including tremors.

series is stored and it can later be analyzed computationally.

speed / position transducers of many types [11; 29].

introduced into the muscle tissue [26; 27; 28; 37].

(synchronous or alternating) are used to evaluate the tremor [38].

electromyography (EMG) and spirography [5]. The biomechanical analysis of the tremor involves qualitative and quantitative aspects, and its main methods of measuring are electromyography (EMG), magnetic tracker system, active optical markers, accelerometers,

The most common method for eletronic evaluation of tremor is the accelerometry, which makes use of sensors to measure the acceleration of a body part [12; 26; 27; 28]. Accelerometers are the main tool for the identification of tremor, easily observed by the large number of recent studies addressing the assessment of tremor [29; 30; 31; 32; 33; 34; 35]. The accelerometers measure linear acceleration forces in three orthogonal directions, being able to capture the movement of members produced by the action of gravity and

In accelerometry, data acquisition is performed by a sensor known as accelerometer that based on the Newton's second law, is capable of measuring the acceleration of a body. The accelerometer consists of an electromechanical device, usually based on the piezoelectric effect or the variation of capacitance which, when attached to any part of the body is capable of measuring acceleration forces or the movement caused by the tremor. This device generates a sequence of values (time-series) representing the instantaneous value of the acceleration as a function of time on the body part in which the sensor has been set. This

Following this same logic (electronic evaluation, storage and computational analysis), other methods have been proposed, such as gyroscopes (evaluation of angular displacement) and

Gyroscopes are devices used to measure angular velocity. It is a simple device to detect the rate of change in the orientation of each segment and are insensitive to gravitational force [36]. Another tool to detect tremor consists in the use of electromyography. The electromyographic signal (EMG) can be considered as the superposition of individual activity of several active motor units during muscle contraction and may be used to diagnose many types of neuromuscular disorders. The EMG signal may be picked up by electrodes placed on the skin surface or by means of needle / wire electrodes which are

Electromyography is an experimental technique concerned with the development, recording and analysis of myoelectric signals. The frequency (Hz), mean amplitude (mV) and pattern

In the acquisition of electromyographic signals for tremor analysis is common to use a specific task with the use of weights to reduce the influence of the heartbeat on the acquired electromyographic signal. For example, Elble (2003) compared the tremor in two groups of healthy individuals, a group of young (20-42 years old) and another group of elderly (70-92 years old). Elble analyzed the signals obtained in a state without load and with the addition of a weight of 300g. In this study, subjects were seated with the forearm supported and hands at rest or under load (palm and fingers extended in a straight line with the forearm).

Furthermore, there are still new devices for tremor evaluation through videos [30] and tools that use accelerometers and transmit information through internet and Bluetooth technology [41]. The magnetic tracker system provides the movement displacement (x, y and z) and orientation (pitch, roll and yaw) of each body segment relative to a fixed transmitter [42]. From the active optical markers can be extracted the acceleration and the application of trigonometry makes possible the description of the vector orientation and the estimation of limb posture [43].

Tremor quantification can be used to control the administration of therapeutic drugs [39] and the optimization of deep brain stimulation [40].

The signal processing and analysis of tremor often involves the spectral analysis, based on Fast Fourier Transform – FFT [35; 39; 41], but this technique as modified weighted Fourier Linear Combiner –WFLC [44] is suitable for periodic or quasi-periodic estimation of motion with single dominant frequency, whereas Band-Limited Multiple Fourier Linear Combiner – BMFLC [34] is suitable for estimation of band limited signals consisting of multiple frequency components. Other methods can also be found as Detrended Fluctuation Analysis (DFA) to analyze hand essential tremor time-series extracted from regions around the first three main frequency components of the tremor power spectra – PWS [45]. To increase the accuracy other modifications or algorithms are used [46; 47]. However, it is not possible to determine the best way to perform these analyses, since this depends on the objectives of the study. Therefore, it is not possible to reach any conclusion on the most appropriate methodologies for the detection and diagnosis of tremor [3].

Hand-drawing patterns are commonly assessed by means of visual rating scales.[48; 49] However, such scales provide only crude subjective estimates of tremor amplitude. In order to reduce the subjectivity and limitation of some methods based on visual scales, there have been developed a few strategies for electronically measuring tremor, such as accelerometry and digitizing tablets. The use of digitizing tablets is common and provides the possibility of tremor activity detection under kinetic conditions.

The usual function of a digitizing tablet is to enable the analysis of drawings directly on the computer. The measurement of tremor by using digitizing tablets is a non-invasive alternative for tremor detection that combines simplicity with the precision and versatility of computational methods. The digitizing tablet is able to inform the position of the tip of the pen on its surface. By using this property this device can detect the movement of a subject following standard drawing patterns placed on it [27; 49; 50; 51; 52; 53; 54; 55; 56]

Subjectively interpreted in previous decades, nowadays the digital spirography can provide quantitative data of the movement control [57]. The spirography has been considered valid and reliable to diagnose early Parkinson's disease [58], essential tremor [59] and to distinguish tremulous parkinsonian patients with normal presynaptic dopaminergic

imaging from tremulous patients with Parkinson's disease [60]. In general, the signals are recorded and stored for posterior analysis. The analysis involves methods such as the radius-angle transformations of the two-dimensional spiral pictures that are captured from the original clinical information (shape, kinematics and dynamics) [57; 58]. In addition, more sophisticated tools and modern statistical algorithms can be used for data evaluation [59; 60].

Human Tremor: Origins, Detection and Quantification 19

The authors would like to express their gratitude to "Coordenação de Aperfeiçoamento de Pessoal de Nível Superior" (CAPES - Brazil), "Conselho Nacional de Desenvolvimento Científico e Tecnológico" (CNPq – Brazil) and "Fundação de Amparo à Pesquisa do Estado

[1] Bhagwath, G. Tremors in elderly persons: clinical features and management. Hospital

[3] Mansur, P. H. G. et al. A review on techniques for tremor recording and quantification. Critical Reviews in Biomedical Engineering, v. 35, n. 5, p. 343-362, 2007. ISSN 0278-

[6] Wyne, K. T. A comprehensive review of tremor: an organized approach to the patient assessment is crucial to reaching an accurate diagnosis. Consider the constellation of signs and symptoms, and know the characteristics of each form of tremor. Journal of the

[7] Jankovic, J. Essential tremor: clinical characteristics. 2000. S21-5 ISBN 0028-3878.

[8] Mcauley, J. H.; Marsden, C. D. Physiological and pathological tremors and rhythmic central motor control. Brain, v. 123, n. 8, p. 1545-1567, August 1, 2000 2000. Disponível

[9] Hallett, M. Overview of Human Tremor Physiology. Movement Disorders, v. 13, n. S3,

[10] Grimaldi, G.; Manto, M.-U.; Manto, M. Tremor: From Pathogenesis to Treatment. San

[11] De Lima, E. et al. Empirical mode decomposition: a novel technique for the study of tremor time series. Medical and Biological Engineering and Computing, v. 44, n. 7, p.

569-582, 2006. Disponível em: < http://dx.doi.org/10.1007/s11517-006-0065-x >. [12] Deuschl, G.; Lauk, M.; Timmer, J. Tremor classification and tremor time series analysis. Chaos, v. 5, n. 1, p. 48-51, 1995. Disponível em: < http://link.aip.org/link/?CHA/5/48/1 >.

< http://www.biomedsearch.com/nih/Essential-tremor-clinical-characteristics/

< http://www.begellhouse.com/journals/4b27cbfc562e21b8,4d8cbde20903daf0,

[4] Borges, V.; Ferraz, H. B. Tremors. Revista Neurociências, v. 14, n. 1, p. 43-47, 2006. [5] Almeida, M. F. S. et al. Investigation of Age-Related Changes in Physiological Kinetic Tremor. Annals of Biomedical Engineering, v. 38, n. 11, p. 3423-3439, 2010. ISSN 0090-

6964. Disponível em: < http://dx.doi.org/10.1007/s10439-010-0098-z >.

American Academy of Physicians Assistants v. 18, n. 12, p. 43-50, 2005.

em: < http://brain.oxfordjournals.org/cgi/content/abstract/123/8/1545 >.

p. 43-48, 1998. ISSN 1531-8257. Disponível em: < http://dx.doi.org/10.1002/mds.870131308 >.

Rafael, California: Morgan & Claypool Publishers 2008.

[2] Smaga, S. Tremor. American Family Physician, v. 68, n. 8, p. 1545-1553, 2003.

de Minas Gerais" (FAPEMIG – MG – Brazil) for the financial support.

**Acknowledgement** 

**5. References** 

Physician, v. 49, p. 31-49, 2001.

940X. Disponível em:

Disponível em:

10854348.html >.

3889d79e52078054.html >.

Digitizing tablet was used by Almeida (2010) [5] with a technique known as spirography. This technique consists in the reproduction by the patient of the Archimedes' spiral according to an ideal model. Thus, a model of this spiral is displayed on the table surface and the patient should try to cover the route of the model as accurately as possible.

Several attributes of the spiral of Archimedes make its use attractive in tests for the detection of human tremor. First, it has a simple design and it is easily understood by subjects who can follow its trajectory. Secondly, the shape of the spiral is smooth with an increasing radius, reducing the occurrence of false-positive tremor caused by abrupt changes in the direction of motion

There are a number of research studies concerning the employment of digitizing tablets for both the quantification of pathological tremor and the detection of movement disorders [49; 50; 51; 52; 53; 54; 55; 56; 61]. However, even with the advances in the technology of digitizing tablets, which allowed for more precision and accuracy in the measurement of movements, no study focusing upon the use of these devices, as a tool for investigating the relation between physiological tremor and ageing in kinetic conditions, was found in our literature survey. Although some authors, e.g., Wenzelburger *et al*.,[62] support the hypothesis that kinetic tremor is related to an enhancement of physiological tremor this assumption is not consensual [26; 27; 63] and therefore additional studies in this area are required.

The different ways of evaluating the tremor, clinical and biomechanics, can be viewed as complementary and in general are used simultaneously, with the aim of compare the qualitative and quantitative data. Thus, it is expected that future improvement of existing tools, as well as the introduction of new tools better clarify this point.
