Motor unit control strategies of endurance- versus resistance-trained individuals

Introduction: We examined motor unit (MU) control properties of resistance-trained (RT) and endurance-trained (ET) individuals. Methods: Five RT (age 25±4 years) and 5 ET (age 19±1 years) subjects participated. Surface electromyography (EMG) data were recorded from the vastus lateralis during isometric trapezoid muscle actions at 40% and 70% of maximal voluntary contraction. Decomposition and wavelet transform techniques were applied to the EMG signals to extract the firing events of single MUs and EMG intensity across the frequency spectrum. Results: There were significant differences between RT and ET for the mean MU firing rate and derecruitment threshold versus recruitment threshold relationships and EMG intensity at various wavelet bands during the linearly increasing, steady force, and linearly decreasing segments of the trapezoid contraction. Conclusions: MU behavior is altered as a function of training status and is likely the result of differences in the physical properties of the MU.