An EMG-to-Force Processing approach for estimating in vivo hip muscle forces in normal human walking

The force of a single muscle is not directly measurable without invasive methods. Yet invasive techniques are not appropriate for clinical use, thus a non-invasive technique that combined the electromyographic (EMG) signal and a neuromuscular model was developed to determine in vivo active muscle forces at the hip. The EMG-to-force processing (EFP) model included active and passive moment components, and the net EFP moment was compared with the hip moment obtained with standard inverse dynamics techniques ("gold standard"). The two methods were compared at percent gait cycle intervals, and the correlation coefficient between methods was excellent (r2=91). The closeness of fit confirms that the approach is a reasonable approximation of net moment and, possibly, individual muscle forces. The greatest estimated hip force was produced by a hip abductor. A novel finding was that the hip adductors did not behave a single synergistic group. The Adductor Magnus synergistically assisted other hip extensors, and produced forces that were out-of-phase with the other hip adductor forces. Rectus Femoris was only active during hip flexion (not knee extension).