Neuromuscular control of a five-finger pinch task is influenced by training history.

Hand control for dexterous and strength-based tasks involves several levels of the neuromuscular system which interact to produce force. We investigated hand force, motor unit (MU) control, and intermuscular coherence in specialist-trained groups to identify how training may affect neuromuscular force control and motor neuron activity. Equal groups of ten strength-trained (rock climbers) and dexterity-trained (musicians) individuals participated. Measures of forearm muscle structure were recorded and used to normalize maximal five-finger pinch force. Several submaximal trapezoidal pinch contractions were performed while force and electromyography (EMG) were recorded, and force steadiness was calculated. Motor unit firing rates were calculated from spike trains identified by surface EMG decomposition. Intermuscular coherence was calculated between two muscles controlling the hand (the abductor pollicis brevis and flexor digitorum superificialis), providing an estimate of the common synaptic inputs to these simultaneously activated muscles. Strength-trained participants had a higher force capacity (even when normalized to muscle size) and were steadier at controlling forces. The dexterity-trained group had faster MU discharge rates in the abductor pollicis brevis muscle at moderate force levels. Measures of synaptic inputs to the motor neuron pools were inconsistent. However, the largest peaks in the beta-band were at the lowest measured force level for the dexterity-trained group, while at the highest force intensity for the strength-trained group. These findings may indicate that the neuromuscular control of hand force differs between groups with different training histories.