Comparison of methods for the calculation of energy storage and return in a dynamic elastic response prosthesis

The standard method used to calculate the ankle joint power contains defici encies when applied to dynamic elastic response prosthetic feet. The standa rd model, using rotational power and inverse dynamics, assumes a fixed join t center and cannot account for energy storage, dissipation, and return. Th is study compared the standard method with new analysis models. First, assu mptions of inverse dynamics were avoided by directly measuring ankle forces and moments. Second, the ankle center of rotation was corrected by includi ng translational power terms. Analysis with below-knee amputees revealed th at the conventional method overestimates ankle forces and moments as well a s prosthesis energy storage and return. Results for efficiency of energy re turn were varied. Large differences between models indicate the standard me thod may have serious inadequacies in the analysis of certain prosthetic fe et. This research is the first application of the new models to prosthetic feet, and suggests the need for additional research in gait analysis with e nergy-storing prostheses. (C) 2000 Elsevier Science Ltd. All rights reserve d.