I. INTRODUCTION
Modern transfemoral prostheses can be classified in three major groups: passive, dynamically damped, and powered, each of which exhibits fundamental deficiencies. Passive and dynamically damped knees are by their nature capable only of negative mechanical power and therefore cannot replicate the generative phases of the natural knee [1]. As a result, the adequate locomotion of aboveknee amputees is impaired; leading to asymmetric gait and elevated metabolic energy consumption relative to healthy subjects [2]–[4].