Effect of Activity on the Visco-Elasticity of Normal and Iodoacetate Muscles

Gasser and Hill's studies 1 on the visco-elasticity of muscle by the damped vibrating spring method have been questioned in subsequent work. 2 , 3 , 4 The present research employs the spring technic, but criticisms of it have been largely overcome by eliminating slack of the muscle at all times, by holding constant the initial length of any muscle subjected to a series of tests, and by limiting visco-elastic comparisons to either states of contraction or rest as modified by previous activity.

Excised, Ringer's-equilibrated Rana pipiens sartorii were used throughout. The muscles (average excised length, 34.8 mm) were stretched) 15% when attached to the undetected spring, and a further 15% stretch occurred with the spring maximally deflected.

In the work reported below, each plotted value represents the average behavior of at least 3 different muscles, and, in general, the mean deviation for the viscosity coefficient values is about ±6%, and for the elasticity coefficient values, about ±12%.

Fig. 1 shows the progressive relative effects of a series of 5 sec. maximum isometric tetani of the normal muscle (the spring acting as the isometric lever) when the visco-elastic determinations were made during 25-sec. rest periods interposed between the tetani. Apart from the initial rise in the viscosity coefficient, the progressive effect of the activity is to cause a general reduction in both the viscosity and elasticity of the resting, gradually fatiguing, muscle.

Fig. 2 presents the changes in the visco-elastic behavior when the determinations are made during each of the 5-sec. tetani of a tetanus series of a normal muscle. Here the viscosity and the elasticity become progressively reduced in the muscle as it becomes more and more fatigued. Thus, whatever the values of the viscosity and the elasticity coefficients in the normal muscle, initially at rest or during the first tetanus, the effect of the development of fatigue is to reduce these coefficients within each of the series of successive contracting or resting states, although, as comparison of Fig. 1 and 2 demonstrates, the course of the changes in the resting series is not paralleled in detail by that in the contracting one.