Modeling of skeletal muscle single twitch

Model of muscle contraction is used to describe a muscle single twitch. An approach based on motion separation method is used to build reduced models of skeletal muscle contraction based on the model of sarcomere contraction. These models have different accuracy of modeling fast transient process. The basic sarcomere contraction model is a system of 7-th nonlinear dif-ferential equations. The integration of this system allowed to construct a simplified model of the 2-nd order, describing the behavior of an assembly of active motor units. The advantage of this model is the good validity of various parameters of the model, including those reflecting the pro-cesses occurring at the cellular level in the muscle. This advantage is due to the choice of a basic sarcomere contraction model, the parameters of which are properly validated. The input signal for reduced models is the average rate of influx of calcium ions in the muscle, which is assumed to be linearly related to the action potential that occurs on motor units in the muscle. Two regimes of muscle contraction are used to simulate skeletal muscle contraction: isometric and isotonic regimes. Muscle contraction due to short stimulation (5 ms) numerically calculated using reduced muscle models. Estimates of the contraction time, time of relaxation phase, and the characteristic values of the concentration of calcium ions in the muscle are calculated. For the frog's sartorius muscle, these characteristics calculated from the models turn out to be close to those observed in experiments. Thus, suggested reduced muscle models allow to describe muscle contraction due to single nerve impulse from muscle motor unit.