Dynamic optimization of human walking

A three-dimensional, neuromusculoskeletal model of the body v was combined with dynamic optimization theory to simulate normal walking on level ground . The body, was modeled as a 23 degree-of-freedom mechanical linkage, actua ted by 54 muscles. The dynamic optimization problem was to calculate the mu scle excitation histories, muscle forces, and limb motions subject to minim um metabolic energy expenditure per unit distance traveled. Muscle metaboli c energy was calculated by summing five terms: the basal or resting heat, a ctivation heat, maintenance heat, shortening heat, and the mechanical work done by all the muscles in the model. The gait cycle tvas assumed to be sym metric; that is, the muscle excitations for the right and left legs and the initial and terminal states in the model were assumed to be equal. Importa ntly, a tracking problem was not solved. Rather only, a set of terminal con straints was placed on the states of the model to enforce repeatability of the gait cycle. Quantitative comparisons of the model predictions with patt erns of body-segmental displacements, ground-reaction forces, and muscle ac tivations obtained from experiment show that the simulation reproduces the salient features of normal gait. The simulation results suggest that minimu m metabolic energy per unit distance traveled is a valid measure of walking performance.