Neuromuscular determinants of force coordination during multidigit grasping.

The biomechanical structure of the hand and its underlying neurophysiology contribute to the coordination of the kinematics and kinetics necessary for multidigit grasping. We recently examined the neural organization of inputs to different extrinsic finger flexors during multi-digit object hold and found moderate to strong motor unit short-term synchrony. This suggests a common neural input to the motoneurons innervating these different hand muscles/muscle compartments, which may in turn influence the coordination of grip forces. To further characterize this common input to the hand muscles during multidigit grasping, we used the frequency-based measure of coherence. Motor unit coherence provides information with regards to the oscillatory frequency of a common input, as well as the coupling of the discharges of a motor unit pair at both short and long latencies. Preliminary results indicate that a large proportion of trials are characterized by significant coherence in the 1-12 Hz frequency range, which is more pronounced in the within- than between-muscle/muscle compartment analysis. This indicates a differential organization of common oscillatory inputs to pairs of motoneurons innervating the same vs. different muscles/ muscle compartments. The functional role of the 1-12 Hz oscillatory modulation of motor unit behavior is currently being investigated.