**1.2 Skeletal muscle changes after hemiparetic stroke**

Evidence has revealed that the mechanisms of abnormal muscle tone in stroke patients include physiologic as well as mechanical (viscoelastic) properties of muscle (Dietz et al., 1981; Katz & Rymer, 1989; Pandyan et al., 1999; Rydahl & Brouwer, 2004). Significant changes in structural and mechanical properties of the paralyzed muscle occur after a stroke (Sjostrom et al., 1980; Svantesson et al., 2000). Muscular atrophy and muscle phenotype shift to fast-twitch fiber proportions in the hemiparetic leg muscle after a stroke and relate to muscle fatigue, poor fitness, poor physical performance, and neurologic gait deficit (Hafer-Macko et al., 2008). Spasticity (hyperactivity of stretch reflexes) and hypertonia (i.e., increased stiffness and viscosity) are common impairments after stroke (de Vlugt et al., 2010; Katz & Rymer, 1989). Spasticity is attributed to increased muscle tone related to hyperreflexia according to Lance (1980) who defined spasticity as a velocity-dependent increase in tonic stretch reflexes (muscle tone) with exaggerated tendon jerks, resulting from reflex hyperexcitability (Lance, 1980). Hypertonia, i.e., increased resistance to passive stretch, was more associated with intrinsic changes of the muscles than increased reflex activity (O'Dwyer et al., 1996). Moreover, the muscle stiffness of the affected leg was much higher than that of the contralateral leg after a stroke, suggesting a difference in the passive mechanical properties of the muscles of the spastic limb compared with the normal limb (Svantesson et al., 2000).

## **2. Methods for measuring muscle tone, elasticity, and stiffness**

In recent decades, new methods, such as botulinum toxin, have been increasingly used to treat spasticity due to stroke (Shaw et al., 2011). Thus, the need for a quantitative measurement of muscle tone in the clinical setting has been highlighted. The development of an adequate tool that is reliable, valid, and responsive to measure the progression of muscle properties and success of treatments becomes urgent (Haas & Crow, 1995).

#### **2.1 Common clinical measure of muscle tone**

The Ashworth Scale (AS) and the Modified Ashworth Scale (MAS) are the most common clinical measures of muscle tone, rating the resistance perceived to passive stretch of the muscle with a 5- or 6-point ordinal scale, respectively (Ashworth, 1964; Bohannon & Smith, 1987; Pandyan et al., 1999). Although they are useful in the clinic, these two measures have been criticized for:


al., 2010), stretching maneuvers (Magnusson, 1998; Reisman et al., 2009), aerobic exercise (Hafer-Macko et al., 2008), the length of skeletal muscle (Ditroilo et al., 2011; Hoang et al., 2007), and eccentric exercise (Hoang et al., 2007; Whitehead et al., 2001). Decreased muscle elasticity brings on easier fatigueability and limited movement speed (Gapeyeva & Vain, 2008). Muscle performing the movement (agonist) stretches out the antagonist muscle. Antagonist muscles with higher stiffness require greater effort for stretching, which leads to

Evidence has revealed that the mechanisms of abnormal muscle tone in stroke patients include physiologic as well as mechanical (viscoelastic) properties of muscle (Dietz et al., 1981; Katz & Rymer, 1989; Pandyan et al., 1999; Rydahl & Brouwer, 2004). Significant changes in structural and mechanical properties of the paralyzed muscle occur after a stroke (Sjostrom et al., 1980; Svantesson et al., 2000). Muscular atrophy and muscle phenotype shift to fast-twitch fiber proportions in the hemiparetic leg muscle after a stroke and relate to muscle fatigue, poor fitness, poor physical performance, and neurologic gait deficit (Hafer-Macko et al., 2008). Spasticity (hyperactivity of stretch reflexes) and hypertonia (i.e., increased stiffness and viscosity) are common impairments after stroke (de Vlugt et al., 2010; Katz & Rymer, 1989). Spasticity is attributed to increased muscle tone related to hyperreflexia according to Lance (1980) who defined spasticity as a velocity-dependent increase in tonic stretch reflexes (muscle tone) with exaggerated tendon jerks, resulting from reflex hyperexcitability (Lance, 1980). Hypertonia, i.e., increased resistance to passive stretch, was more associated with intrinsic changes of the muscles than increased reflex activity (O'Dwyer et al., 1996). Moreover, the muscle stiffness of the affected leg was much higher than that of the contralateral leg after a stroke, suggesting a difference in the passive mechanical properties of the muscles of the spastic limb compared with the normal limb

**2. Methods for measuring muscle tone, elasticity, and stiffness** 

**2.1 Common clinical measure of muscle tone** 

muscle properties and success of treatments becomes urgent (Haas & Crow, 1995).

not standardizing stretch velocity in manual testing (de Vlugt et al., 2010),

not providing an assessment of activated muscle tone (Sommerfeld et al., 2004),

not quantifying resistance in absolute units (Pandyan et al., 1999),

In recent decades, new methods, such as botulinum toxin, have been increasingly used to treat spasticity due to stroke (Shaw et al., 2011). Thus, the need for a quantitative measurement of muscle tone in the clinical setting has been highlighted. The development of an adequate tool that is reliable, valid, and responsive to measure the progression of

The Ashworth Scale (AS) and the Modified Ashworth Scale (MAS) are the most common clinical measures of muscle tone, rating the resistance perceived to passive stretch of the muscle with a 5- or 6-point ordinal scale, respectively (Ashworth, 1964; Bohannon & Smith, 1987; Pandyan et al., 1999). Although they are useful in the clinic, these two measures have

worse economy of movement (Gapeyeva & Vain, 2008).

**1.2 Skeletal muscle changes after hemiparetic stroke**

(Svantesson et al., 2000).

been criticized for:


The reliability and validity of both scales have also been questioned (Aarrestad et al., 2004; Katz & Rymer, 1989; Leonard et al., 2003; Pandyan et al., 1999; Pomeroy et al., 2000).

The AS has only been validated for measuring spasticity around the elbow after stroke (Lee et al., 1989). The MAS is reliable for measuring muscle tone in certain muscle groups, such as the elbow, wrist, and knee flexors, in stroke patients (Gregson et al., 2000). These critiques and limitations reaffirm the need for identifying suitable clinical tools that reliably and accurately assess the biomechanical properties of muscle, including tone, elasticity, and stiffness (Pandyan et al., 1999).

## **2.2 Laboratory measure of mechanical properties of muscle**

The mechanical properties of muscle are generally assessed in laboratories with expensive and heavy equipment, such as isokinetic and ultrasound machines (Ditroilo et al., 2011). Ultrasonography is limited to superficial structures and does not assess specific muscle mechanical properties (Nordez et al., 2008).

#### **2.3 A new novel instrument for measuring muscle tone, elasticity, and stiffness simultaneously**

For clinical applications, mechanical properties, such as muscle elasticity and stiffness, may not be accurately estimated by the clinical scales. A novel hand-held myotonometer, the Myoton myometer (Müomeetria AS, Tallinn, Estonia) device, provides painless and noninvasive means to obtain quantitative and objective assessments of mechanical properties of muscles (Gapeyeva & Vain, 2008; Roja et al., 2006). The Myoton myometer was primarily developed for testing the superficial skeletal muscles (Gapeyeva & Vain, 2008). The principal differences between myotonometry and traditional measures of muscle tone are that the former measures the tone, elasticity, and stiffness simultaneously and quantitatively (Gapeyeva & Vain, 2008), is not affected by tester strength (Leonard et al., 2003), and is more sensitive to detect small changes (Aarrestad et al., 2004; Leonard et al., 2001). The myotonometer has the additional advantages of an appropriate size for being portable, relatively inexpensive and convenient to use, and relatively easy to administer over a wide range of postural or extremity musculature (Aarrestad et al., 2004; Ditroilo et al., 2011; Gapeyeva & Vain, 2008; Gubler-Hanna et al., 2007; Ianieri et al., 2009).

Muscle properties can be measured with the myotonometer without the muscle being moved, which might be helpful with patients who have limited range of motion or pain with movement (Leonard et al., 2003). Its application leads to a more objective assessment of numeric parameters of muscle tone, elasticity, and stiffness within minutes (Aarrestad et al., 2004). Therefore, the myotonometer appears to be clinically applicable without compromising the precision related to more complex laboratory methods and ensures a better pathophysiologic vision of all three muscle properties.

Myotonometric Measurement of Muscular Properties of Hemiparetic Arms in Stroke Patients 41

Our recent study (Chuang et al., 2012) addressed the test-retest reliability, validity, and responsiveness of the Myoton-3 myometer used for assessing tone, elasticity, and stiffness of the affected forearm muscles under a relaxed state in stroke rehabilitation. The Myoton-3 myometer represents a new technology to quantify mechanical properties of resting and contractiling muscles. To the best of our knowledge, this was the first report to show the metric soundness of the Myoton-3 myometer for assessing muscle tone, elasticity, and stiffness of the extensor digitorum, flexor carpi radialis, and flexor carpi ulnaris muscles in patients with stroke. Information reported in this study that is relevant to purposes of this

We recruited 67 patients (40 men and 27 women) who were a mean age of 54.67 (SD, 10.90) years. The mean time since the stroke onset was 21.12 (SD, 13.63) months, and 31 patients had left hemiplegia. All participants had sustained a first-ever stroke, Brunnstrom stage III to V for the proximal and distal upper extremity (UE) (Brunnstrom, 1970), MAS ≤ 2 in any joint of the UE (Bohannon & Smith, 1987), no cognitive impairment (Mini-Mental State Examination score ≥ 24) (Folstein et al., 1975), not participated in any experimental rehabilitation or drug studies, and not used anti-spasticity drugs for the UE musculature (e.g., botulinum toxin type A) during the study period. Institutional Review Board approval was obtained from the study

The functional state of the participants' skeletal muscles was assessed by using myotonometric measurements with the Myoton-3 myometer, created at the University of

The Myoton-3 myometer has a two-armed lever. On the long lever is the testing end and on the short lever is the core of the electromagnet. The essence of the method lies in giving the muscle a short mechanical impulse to evoke decaying oscillations of the muscle because of the elastic behavior of the muscle. The working principles of the Myoton-3 myometer were as follows: the testing end of the Myoton-3 was placed perpendicular to the skin surface above the muscle to be measured and a brief mechanical impulse was applied, shortly followed by a quick release to the muscle through an acceleration probe. The characteristics of the muscle deformation and also the damped oscillations of the muscle evoked after the quick release of the testing end were recorded by the acceleration transducer at the testing end of the device. At the moment the Myoton-3 myometer pickup has created the maximum compression of the tested muscle, the corresponding acceleration amax characterizes the

The parameters of the graph characterize the functional state of the muscle. Displacement (s) is the difference in the initial position of the tested muscle and its final position. The relationships between position, velocity, and acceleration form an important application of the definite derivative. The velocity is defined by the derivative of position at a given time; whereas the acceleration is defined by the derivative of velocity at a given time. The average velocity of the muscle is the total displacement during an extended period of time, divided by that period of time. Average acceleration is the total change in velocity over an extended

sites, and written informed consent was obtained from each patient before inclusion.

resistance force of the muscle for the deformation depth Δ*l* (Figure 1).

book chapter is summarized below.

**4.1 Study sample** 

**4.2 Instrument** 

Tartu in Estonia (Vain, 1995).

From discerning muscular properties using myotonometric measurements, clinicians would be able to have a better understanding of the pathologic processes of muscle functions in individuals with spastic muscle secondary to stroke, design a specific rehabilitation program for each patient, make appropriate clinical decision, plan a more targeted and customized treatment specifically for each patient with abnormal muscle properties, and assess the efficacy of specific therapeutic treatment (Pandyan et al., 1999; Wade, 1992). This chapter will illustrate the metric properties of myotonometric measurement based on previous studies and our recent research in stroke rehabilitation.
