Coordination of Voluntary Residual Muscle Contractions in Transtibial Amputees: a Pilot Study.

Recently there has been considerable interest in the use of electromyography (EMG) for the control of powered, lower-limb prostheses. However, little is understood regarding amputee residual muscle, specifically the ability for lower-limb amputees to coordinate previously antagonist residual muscles for different control tasks. In this study, we aimed to investigate the capability of transtibial amputees in coordinating residual gastrocnemius and tibialis anterior for performing a high-level task. Specifically, we examined how three transtibial amputees and one ablebodied subject used residual and intact ankle muscles to balance a virtual inverted pendulum. Subjects controlled the pendulum by modulating stiffness of the base joint proportional to the level of EMG signal exerted. We conducted ten trials for each subject and quantified success of task performance by area of overall sway and number of falls (termed failure). Amputees successfully reduced number of failures, though not to the extent of able-bodied subjects. Interestingly, while able-bodied subjects reduced overall pendulum sway, amputees did not. EMG coordination patterns that preceded failure for amputees were different than that of able-bodied subjects. These results suggest that amputees have altered ability to coordinate muscle post-amputation; however, all subjects can improve the task performance and learn to reduce EMG coordination patterns that led to task failure. Further study is required to investigate the limit of amputees in learning of coordination between antagonist residual muscles in order to inform future neural control of prosthetic legs.