An all purpose computer algorithm used in the analysis and simulation of human locomotion is presented. The utility of the program "DYAMUS" stems from its simplicity in defining the initial configuration of the human model through a configuration graph called the "tree-array," and the handling of individual cases of human locomotion through separate sets of constraints conditions. Both the forward and inverse dynamical problems are presented together with the accommodation of kinematical experimental data. Closed-loops, linear and nonlinear springs and dampers at the joints, friction forces, and other external forces are easily incorporated. The selection of mathematical constraint equations to predict the human behavior during normal walking (gait) is presented. The intention of this paper is to emphasize how the constraints equations play a major role in the simulation of human locomotion once the dynamical equations of motion for a particular model are developed.