Neuromuscular responses of recreationally active women during a sustained, submaximal isometric leg extension muscle action at a constant perception of effort.

Purpose: The purpose of the present study was to examine the fatigue-related patterns of responses for electromyography (EMG), mechanomyography (MMG), and force during a sustained, submaximal isometric leg extension muscle action anchored at RPE = 5.
Methods: Ten women (23.1 ± 2.3 year) performed two, maximal voluntary isometric contractions (MVIC) prior to and following an isometric muscle action that was sustained at RPE = 5 (OMNI-RES) for a maximal time-limit of 5 min or until RPE = 5 could not be maintained (actual time-limit). EMG amplitude (AMP), EMG mean power frequency (MPF), MMG AMP, MMG MPF, and force values were determined every 5% of the actual or maximal time-limit. Regression analyses were used to examine the neuromuscular parameters and force vs. time relationships.
Results: The pretest MVIC (46.9 ± 8.9 kg) was significantly (p = 0.003; d = 1.8) greater than posttest (36.4 ± 5.3 kg) MVIC. The actual time-limit was 180 ± 90.9 s (range 84.8-300 s). The percent decline in force production during the sustained isometric muscle action was 34.7 ± 17.1%, and there was a significant negative, quadratic force vs. time relationship (p < 0.001; R = - 0.983). There was a significant positive, quadratic MMG AMP vs. time relationship (p < 0.001; R = 0.852), but no significant (p > 0.05) relationships for EMG AMP, EMG MPF, or MMG MPF vs. time.
Conclusions: The current findings indicated that it was necessary to reduce force to maintain RPE = 5. The neuromuscular and force responses supported the RPE clamp model and suggested that force was initially regulated by anticipatory feedforward mechanisms and then altered by afferent feedback.