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

PurposeTo investigate whether short-term learning of a new motor task is mediated by changes in common synaptic inputs to motor neurons within and between synergistic muscles. MethodsSeventeen healthy individuals performed 15 repetitions of a complex force-matching task at 10% of a 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 their constituent motor unit spike trains, with individual motor units being 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. ResultsForce-target matching improved across trials, accompanied by a significant decrease in the coefficient of variation of the inter-spike interval (p < 0.01), while the mean discharge rate remained similar (p > 0.85). The area under the curve within delta (p < 0.003) and alpha (p < 0.004) bands decreased between trials, with no significant changes in the beta band (p > 0.05). Notably, reductions in the alpha band correlated significantly with performance improvements in VL (R = 0.81) but not in VM (R = 0.12). ConclusionThe acquisition of a new motor task is mediated by modulations in common synaptic inputs to motor units, leading to improved force control. Our findings further suggest that these changes in common synaptic inputs, particularly in the alpha band, differ between VM and VL.