A powered ankle-foot prosthesis and associated methods of use are described herein. Such prostheses can employ an actuator and elastic components, the actuator being controlled to deliver net positive work to propel the wearing amputee forward and the elastic components being used to store and release negative energy to improve efficiency. Elastic components can be linear springs coupled with a cam and configured in parallel to the actuator. The cam profile can be designed to generate a desired spring torque versus angle curve rather than a spring stroke versus angle curve, thereby reproducing human ankle controlled dorsiflexion stiffness. Such configurations improve system energy efficiency and reduce both actuator torque and power requirements. Such prostheses can also operate in a passive mode, in which a nearly normal gait can be achieved even without powered assist.
