Fig. 1. The method for calculating joint moments, M, and powers, P_m. Joint moment (A) is the product of the magnitude of the ground reaction force, GRF, and the out-moment arm, R. R is the orthogonal distance from the GRF to the center of rotation of the joint. Arrows indicate the direction of positive net moments produced by muscles at a joint. Joint angles were measured as indicated in B. Joint velocities were calculated from the time derivative of the angle () change. The arrows denote the direction of positive velocities. Definitions: a, ankle; h, hip; k, knee; t, toe.