Inter- And Intra-individual Differences In Neuromuscular Responses During Submaximal Leg Extension Exercise

Neuromuscular responses are often reported as composite (mean of all subjects) data to make inferences about fatigue-induced changes in motor unit activation strategies. However, electromyographic (EMG) and mechanomyographic (MMG) signals have demonstrated inter-individual differences in the patterns of responses. PURPOSE: To examine the inter- and intra-individual differences in the EMG and MMG amplitude (AMP) and mean power frequency (MPF) responses during the bilateral leg extension (LE) exercise. METHODS: Eleven men completed a one-repetition maximum (1RM) for the LE (87±16 kg) and repetitions to failure at 70% 1RM (61±11 kg; 15±2 repetitions) on separate days. The EMG and MMG signals were measured from the vastus lateralis of the right and left limb. Polynomial regression analyses were used to determine individual (IND) and composite (COMP), normalized EMG and MMG, AMP and MPF response (linear, quadratic, cubic) vs. percent of total repetitions completed (10-100%). RESULTS: For the COMP EMG AMP, there was a positive, quadratic relationship for the right (R=0.992, p