Exploring Control Mechanism of Motoneuron Pools for the Forearm Antagonist Synergistic Muscles

The EMG-based neural control strategy provides technical support and innovative methodologies for the precise control and natural movement of hand prostheses. For enabling the prostheses to mimic the function of the human hand, it is essential to fully understand the principle of neuromuscular control of human hand. However, we still have little knowledge regarding the functional significance of the proportion of common or independent neural input to the antagonist muscles in extensor and flexor during performing different tasks. Therefore, we used a discharge coherence analysis of motor unit (MU) spike trains to investigate different sources of common and independent input between extensor and flexor muscle groups in different hand gestures. 14 gestures were selected, including the extension of individual and multi fingers, as well as pinch finger tasks. The MU spike trains were obtained from the decomposition of high-density surface electromyography (HD-sEMG) recordings using fastICA. The proportion of the independent neural input to extensor or flexor muscle groups was calculated by the ratio of residual coherence to total coherence. The results showed that the two muscle groups are comparable in independent proportion within each muscle group with relatively greater values in the extensor muscle. The degree of common input shared between the two muscle groups exhibited the highest level (around 35%) in the delta band (1-4Hz) compared to a very small proportion (<13%) in the other frequency bands. Additionally, a significant difference was observed in little finger extension and hand close tasks compared to other hand gestures. Overall, the varied proportions of independent neural input across hand gestures and among muscle groups illustrate the precise neural modulation involved in the co-contraction of the flexor and extensor muscles during flexible hand movements, as observed through the microscopic view of motoneurons.