There is a growing interest in predicting the gait motion of real subjects under virtual conditions, e.g., to anticipate the result of surgery or to help in the design of prosthetic/ orthotic devices. To this end, the motion parameters can be considered as the design parameters of an optimization problem. In this context, determination of the joint efforts for a given motion is a required step for the subsequent evaluation of cost function and constraints. In the double-support phase of gait, the ground reaction forces include twelve unknowns, rendering the inverse dynamics problem indeterminate if no force plate data are available. In this paper, several methods for solving the inverse dynamics problem of the human gait during the double-support phase, using force plates or not, are presented and compared.