Muscle Synergies are Robust across Participants in Upper Limb Rotational Motion

Muscle synergies are defined as the specific co-activation of muscle groups to accomplish function level targets. The hypothesis of muscle synergies helps simplify the motor coordination problem by decreasing the numbers of central nervous system signals. The purpose of this research was to discuss how muscle coordination works across different individuals during the performance of a cyclic movement at specific force levels. We acquired Electromyography (EMG) signals from seven right upper-limb muscles of four participants as they operated the hand-cycle ergometer. Non-negative matrix factorization (NNMF) was used to extract muscle synergies from the EMG signals and compared across the participants at a specific power level. We found that five synergies were shared across participants. Also, the recruitment profile for those synergies appeared to be similar with only slight deviations. Therefore, we conclude that during a constrained rotational motion at constant speed (50 r.p.m) and constant power level (20 watts), the muscle synergies were preserved across participants. The results of this study would be useful in designing assistive devices for rehabilitation purposes.