Ankle-foot orthoses (AFOs) are used in people who have difficulty of working as ankle contracture splints and foot drop splints. Although utilization of AFOs has been expanding, it is still questionable if functions and structures of AFOs are suitable. In this paper, a new active ankle-foot orthosis (AAFO), which is dynamically controlled linked with muscle activities, is proposed. To discuss functions of the AAFO, using the electromyographies (EMGs), muscle activities during dynamic balancing of a body and changing of muscle activities with fatigue are considered. As the results, it's shown that to assist femoris muscles additionally to the tibialis anterior muscle is important as the function of the AAFO.
