Impulse and moment of impulse in the leg joints by impact from kicking.

In a previous paper we have given a theoretical analysis of the impulsive motion of the leg, modeled as a double pendulum. This analysis made it possible to estimate the impulsive reactions in the knee joint as a function of the measured initial and final velocities of the leg, when an impact was given to the lower leg, e.g., by means of a kick. This estimation was made under the assumption that no impulsive moments occur in the hip and the knee joints, i.e., that no muscles were stretched during the time of impact. In the present paper it is shown how such impulsive moments, should they occur, can be determined by means of an additional measurement, i.e., of the velocity of the ball after the impact. The results from a series of experiments are reported, showing that such impulsive moments in the joints occur in an appreciable number of the kicks, especially in the hip joint, indicating that muscles, acting on this joint, are prestressed during the impact.