**1. Introduction**

36 Rehabilitation Medicine

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Stroke is the leading cause of functional disability. The most significant impairment developed in individuals with stroke is the loss of normal skeletal muscle tone on the affected side, which leads to the lack of normal, controlled movements and further limits the individual's ability to carry out tasks of daily living. Session 1 of this chapter describes skeletal muscle changes after stroke and defines functional roles of muscle tone, elasticity, and stiffness. Session 2 discusses methods for measuring muscle tone, elasticity, and stiffness, including common clinical measure, laboratory measure, and a new novel myotonometer. Session 3 presents metric properties of the myotonometric measurements in previous studies. Session 4 provides an overview of myotonometric measurement relevant to stroke motor rehabilitation and future research directions, with special attention on the reliability, validity, and sensitivity to treatment-induced change of using the myotonometer to measure muscle properties of relaxed extensor digitorum, flexor carpi radialis, and flexor carpi ulnaris muscles in patients with stroke. Session 5 concludes the clinical value of myotonometric measurements in stroke rehabilitation.

#### **1.1 The definition and functional role of muscle tone, elasticity, and stiffness**

Muscle tone involves active tension and passive (resting) intrinsic viscoelastic tone (Ditroilo et al., 2011; Masi & Hannon, 2008; Simons & Mense, 1998). Human resting muscle tone was defined as the passive tonus or tension of skeletal muscle that derives from its intrinsic molecular viscoelastic properties (Masi & Hannon, 2008); that is, resting muscle tone is the viscoelastic stiffness without contractile activity (Simons & Mense, 1998). The functional roles of passive muscle tone are for maintaining balanced stability posture and for achieving energy-efficient costs for prolonged duration without fatigue (Masi & Hannon, 2008).

Muscle elasticity is defined as the property of a muscle to return to its original form or shape after removing a deforming force, and muscle stiffness is a muscle's resistance to deformation (Masi & Hannon, 2008; Panjabi, 1992; Simons & Mense, 1998). Factors that affect resting muscle tone, elasticity, and stiffness include neuromuscular disorders (Alhusaini et al., 2010; Hafer-Macko et al., 2008; Ratsep & Asser, 2011), massage (Huang et

Myotonometric Measurement of Muscular Properties of Hemiparetic Arms in Stroke Patients 39

subjectively grading and clustering of scores (Katz & Rymer, 1989; Pandyan et al., 1999),

The reliability and validity of both scales have also been questioned (Aarrestad et al., 2004;

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

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

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.,

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

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

2011; Gapeyeva & Vain, 2008; Gubler-Hanna et al., 2007; Ianieri et al., 2009).

better pathophysiologic vision of all three muscle properties.

 lacking sensitivity for detecting smaller degrees of changes in spasticity (Lance, 1980), poor discrimination between increased muscle tone and soft-tissue stiffness (de Vlugt et

only being applicable for the extremities (Leonard et al., 2001),

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

lacking correlation with functional changes after treatment (Ward, 2000).

Katz & Rymer, 1989; Leonard et al., 2003; Pandyan et al., 1999; Pomeroy et al., 2000).

al., 2010; Sheean & McGuire, 2009), and

stiffness (Pandyan et al., 1999).

**simultaneously** 

mechanical properties (Nordez et al., 2008).

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