Objective: The purpose of the present study was to examine the fatigue-induced changes in torque, and the electromyographic (EMG) and mechanomyographic (MMG) responses during a sustained submaximal, isometric forearm flexion muscle action anchored to a constant rating of perceived exertion (RPE). Methods: Eleven women (mean ± SD: age = 20.5 ± 1.9 yrs.; height = 169.9 ± 6.6 cm; body mass = 73.2 ± 15.9 kg) performed 2, 3s forearm flexion maximal voluntary isometric contractions (MVIC) before a sustained isometric muscle action anchored to RPE = 7 until task failure (defined as torque that would require RPE > 7, or the torque was reduced to zero). The EMG amplitude (AMP), EMG mean power frequency (MPF), MMG AMP, and MMG MPF signals from the biceps brachii (BB) were recorded. Regression analyses were conducted to examine the torque and neuromuscular responses vs. time relationships. Results: The percent decline in torque during the sustained isometric muscle action was 95.69 ± 6.54 %. There was a significant (p < 0.001; R = -0.998), negative quadratic EMG AMP relationship and a significant (p < 0.046; R = 0.952), positive quadratic MMG AMP relationship vs. Time, but no significant (p > 0.05) relationships for EMG MPF or MMG MPF vs. Time. Conclusion: The findings suggested that torque was initially regulated by an anticipatory feedforward mechanism and continually adjusted due to afferent feedback. In addition, substantial inter-individual, as well as differences between the individual and composite responses, were observed for the neuromuscular response patterns.



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