Should prosthetic feet be designed to maximize energy storage and return?

Researchers and manufacturers often tout the energy storage and return in their passive prosthetic foot designs, but limited evidence suggests that more energy is necessarily advantageous for mobility. In this project, we utilized a custom variable-stiffness ankle prosthesis that enabled subjects to select their preferred ankle stiffness, while measuring the mechanical energy stored and returned at five ankle stiffness levels within 20% of a user-selected preferred stiffness. Mechanical energy storage was highest at the lowest tested stiffness levels, suggesting wearers did not prefer the ankle prosthesis stiffness that led to maximal energy storage.Consequently, caution should be used when advocating for increased energy storage and return as a benefit of modern passive ankle-foot prostheses.