Hysteresis in the electromyography–force relationship: Toward an optimal model for the estimation of force

INTRODUCTION: In this study we analyzed the presence of hysteresis in the relationship between features of electromyography (EMG) and force. METHODS: Intramuscular EMG and surface EMG (sEMG) were recorded concurrently from the flexor digitorum profundus muscle from 0% to 100% maximum voluntary contraction (MVC) in 11 subjects. Two features, mean absolute value (MAV) and Wilson amplitude (WAMP), were computed using either the first-order (poly1) or third-order (poly3) polynomial. RESULTS: We detected hysteresis in the EMG-force relationship for both features in all subjects. In general, the hysteresis-based models performed better than the overall model (which does not take into account the hysteresis in the EMG-force relationship), with R(2) values about 0.98 (averaged across subjects) and root mean square error around 5% of the MVC force. CONCLUSION: These results imply the existence of a path-dependent model, which may improve the accuracy of force estimation. Muscle Nerve, 2012.