A mathematical model of skeletal muscle and numerical simulations of its response under stretching

A mathematical model is formulated for activated muscles under stretching. "Yielding", which is characterized as the decrease in the rate of muscle fo rce during stretching, is reported in the literature for activated cat sole us muscles. We hypothesize that such '"yielding" mainly results from the ch ange of an active state that is determined by step functions of activation stimulus which reflects the properties of muscle conditions. The activation stimulus increases when the muscle begins to be stretched, and it decrease s after a short duration at the start of stretching and when the stretching is stopped. The effect of velocity and stimulation rate is expressed by de termining the change of activation stimulus systematically. The simulation results show that the "'yielding" is described by a simple frame of the mod el. The model might be applied to simulate the behavior of activated muscle s during stretching such as walking and sports.