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

PurposeThe 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.MethodsTen women (23.12.3year) 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 5min 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.ResultsThe pretest MVIC (46.9 +/- 8.9kg) was significantly (p=0.003; d=1.8) greater than posttest (36.4 +/- 5.3kg) MVIC. The actual time-limit was 180 +/- 90.9s (range 84.8-300s). 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.