The physiological energy requirements of prosthetic gait in above-knee amputees have been observed to be significantly greater than that for normal healthy gait. Existing models of energy flow during walking, however, have not been very successful in explaining the reasons for this additional energy cost. In this paper, a new method is developed that estimates the physiological cost of walking using a multi-body dynamic model and a muscle stress based estimate of metabolic energy cost. A distinctive feature of the method is a balance controller component that dynamically maintains the stability of the model during the walking simulation. This allows for a forward dynamic analysis of many consecutive steps, and includes the metabolic cost of maintaining balance in the model. An optimization algorithm is then applied to the joint kinematic patterns to find the optimal walking motion for the model. This approach allows the simulation to find the most energy efficient gait for the model, mimicking the natural human tendency to walk with the most efficient stride length and speed. When applied to simulations of both able-bodied and amputee models, the results indicate a higher physiological cost for the amputee model, suggesting that this method more accurately represents the relative metabolic costs of able-bodied and amputee walking gait.
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