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<0.001) and left limbs (R=0.984, p=0.044). For the COMP EMG MPF, there was a negative, cubic relationship for the right limb (R=-0.982, p=0.001) and a negative, quadratic relationship for the left limb (R=-0.950, p=0.008). For the COMP MMG AMP, there was a positive, quadratic relationship for the right limb (R=0.982, p=0.004) and a positive, linear relationship for the left limb (r=0.942, p<0.001). Both the right (r=-0.842, p=0.001) and left limbs (r=-0.901, p<0.001) demonstrated a negative, linear relationship for the COMP MMG MPF. For the IND EMG AMP and MPF, 9-27% of the subjects demonstrated the same response as the COMP, 36-55% demonstrated different patterns, and 36-45% demonstrated no relationship. For the IND MMG AMP and MPF, 27-45% of the subjects demonstrated the same response as the COMP, 9-36% demonstrated different patterns, and 36-55% demonstrated no relationship. CONCLUSIONS: While most subjects demonstrated a similar direction, less than 50% demonstrated the same pattern of response for EMG or MMG, AMP and MPF signals as the COMP data for both limbs. Thus, individual responses should be considered when making inferences about motor unit activation strategies from neuromuscular responses during fatiguing resistance exercise. ABSTRACT FROM AUTHOR
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Dinyer, T. K., Soucie, E. P., Succi, P. J., Voskuil, C. C., Byrd, M. T., & Bergstrom, H. C. (2021). Inter- And Intra-individual Differences In Neuromuscular Responses During Submaximal Leg Extension Exercise. Medicine & Science in Sports & Exercise, 53(8S), 43–43. https://doi.org/10.1249/01.mss.0000759576.78338.64
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