For a lower-limb prosthesis, the primary purpose is to restore the locomotive functions of lost limb sections and joints. Traditionally, such functions have been restored by energetically passive (i.e., unpowered) devices. The passive nature of such devices is fundamentally different from the energetic role of the corresponding biological joints, and thus poses a significant limitation to their functionality and rehabilitation effects. For example, biomechanical studies on human locomotion highlight the important energetic role of the ankle joint. In level walking, the ankle produces substantially more work than the knee and hip [1]. Without the power generated by the ankle, an amputee fitted with passive transtibial (TT) prosthesis has to expend more power on the unaffected biological joints to compensate for the lack of power generation in the prosthetic ankle, resulting in an asymmetric gait and greater energy consumption [2].
To address this important issue, a considerable...
