Differential changes in the effective neural drive following new motor skill acquisition between vastus lateralis and medialis

PURPOSE: To investigate whether short-term acquisition of a new motor task is mediated by changes in common synaptic inputs to motor neurons within and between synergistic muscles. METHODS: Twenty one participants performed 15 repetitions of a complex force-matching task at 10% of maximal voluntary contraction. Two trials were selected for analysis, the one with the highest force-target error (pre-learning) and the one with the lowest (post-learning). High-density surface electromyograms recorded from vastus medialis (VM) and vastus lateralis (VL) were decomposed into motor unit spike trains, and units were tracked between trials. Motor unit discharge behavior and common synaptic oscillations across the delta, alpha, and beta bands were calculated and compared between pre- and post-learning. RESULTS: Force-target matching improved across trials, accompanied by a significant decrease in discharge rate variability in VL (p < 0.001), while the mean discharge rate remained similar (p > 0.14). The area under the curve in delta band coherence decreased for VM (p = 0.01), VL (p < 0.001) and VM-VL motor units (p < 0.001). In contrast, alpha band decreased for VL (p < 0.001), but not for VM (p = 0.41). Notably, reductions in alpha band correlated significantly with performance improvements only in VL (R = 0.77) but not VM. CONCLUSION: The acquisition of a new motor task is mediated by modulations in common synaptic inputs to motor units, leading to improved force control. Our findings suggest muscle-specific associations between these changes in common synaptic inputs and short-term motor learning, particularly in the alpha band.