Most current knowledge concerning the mechanical behavior of skeletal muscle has been obtained from experiments in which the muscle is impulsively activated (twitch) or maximally activated (tetanus). In living organisms, however, muscle usually functions under conditions of gradually varying partial activation. In the present work equations are derived for partially activated whole muscle which relate the force exerted by the muscle, its contraction, velocity of contraction, and level of neural activation. This is accomplished by considering the sarcomere as the basic contractile unit; by describing its behavior according to a model due to Hill [8]; and predicting muscle behavior by integrating from the sarcomere through the fibril and the fiber to the whole muscle. When this is done it turns out that the model muscle is rather more complex than anticipated. The results should prove useful in modeling skeletal muscle for clinical purposes.

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