Dance Anatomy & Kinesiology

36 Dance Anatomy and Kinesiology

an associated nerve. The classic response of muscle

to this stimulus is to produce tension or contract.

The properties of extensibility and elasticity can be

better understood if we look at a mechanical model

of muscle.

The Mechanical Model of Muscle

A three-component mechanical model has been

developed to explain the behavior of muscle (figure

2.1). The ability of muscle to contract resides within

very small protein structures found within the muscle

cell that are further discussed in the next section of

this chapter. These structures are termed the contrac-

tile component (CC) or active component of muscle.

However, muscle also contains two elastic compo-

nents—the parallel elastic component and the series

elastic component. The contribution of these elastic

components does not require active contraction, and

hence they are also termed passive components. As

its name suggests, the parallel elastic component

(PEC) lies parallel to the contractile component and

is composed of many structures including the con-

nective tissue in muscle, the muscle cell membrane

(sarcolemma), and an elastic protein closely associ-

ated with the contractile proteins of muscle (titin).

Conversely, the series elastic component (SEC) lies

in series with the contractile component and consists

primarily of the tendon (about 85%), with a much

smaller contribution from some of the structures

of the contractile component (Alter, 2004; Enoka,

2002; Kreighbaum and Barthels, 1996; Levangie and

Norkin, 2001).

These elastic components can be modeled as a

spring (figure 2.2), and mechanical energy that is

stored in the elastic component of muscle when a

stretch is applied can be recovered when the stretch

is released (recoverable deformation), just as a spring

will quickly recoil to its unextended position when

the tension is removed. These elastic components

give rise to muscle’s property of elasticity. Elasticity is

the ability of a muscle to return to its resting length

after being stretched. In addition, the connective

tissue associated with muscle has another property,

termed viscosity. Viscous or plastic properties are

usually modeled by a hydraulic cylinder (dash pot)

as shown in figure 2.2 and reflect puttylike behavior,

in which the elongation produced by a force remains

after the force is removed (permanent deformation).

Together, the elastic and viscous properties of con-

nective tissue are termed viscoelastic, and it is this

viscoelastic response that gives rise to muscle’s prop-

erty of extensibility as seen in figure 2.3. Extensibility

or distensibility is the ability of muscle to be stretched

or to increase in length beyond resting length. The

average muscle fiber can be stretched 1.5 times its

resting length (Hamilton and Luttgens, 2002). The

FIGURE 2.1 Three-component mechanical model of

muscle.

FIGURE 2.2 Viscoelastic properties of connective

tissue.