The role of electromechanical delay in modelling the EMG-force relationship during quasi-dynamic contractions of the upper-limb.

There is a discontinuity in published electromechanical delays (EMD) in upper-limb muscles and the state-of-the-art in modelling end-point force from electromyographic signals collected from one or more muscles. Published values are typically in the range of 10 to 30ms, depending on the nature of the contraction. In published literature where the EMG-force relationship is modelled, generally a delay of 100ms or more is induced during linear enveloping to match the EMD. The implications of EMD on end-point force prediction were considered using inter-session end-point force modelling with a support-vector-regression model. The delays were estimated using the first-order cross-correlation and the force and EMG signal were temporally aligned. The results show the delays vary by 20ms or more but did produce a notable trend based on elbow joint angle. We conclude that for upper-limb biomechanics modelling, the best practice is to align the force and EMG signals based on the induced delay during linear enveloping.