Neuromuscular Responses And Perceived Factors Following A Sustained Task Anchored To A Low Perceptual Intensity

PURPOSE: Few studies have examined the effects of a sustained, isometric forearm flexion task (SIFFT) anchored to a low rating of perceived exertion (RPE) on torque and neuromuscular responses, and the perceived sensations (PS) and psychological factors (PF) that contributed to task termination. Thus, this study examined the effects of a SIFFT anchored to an RPE of 4 (RPE = 4) on torque and neuromuscular responses, and the PS and PF that contributed to task termination. METHODS: Twelve men (mean ± SD: age = 20.9 ± 2.2 yrs, height = 179.8 ± 5.3 cm, body mass = 80.2 ± 9.9 kg) performed forearm flexion maximal voluntary isometric contractions (MVIC) before and after a SIFFT to failure (torque reduced to zero) anchored to RPE = 4. Electromyographic (EMG) and mechanomyographic (MMG) signals were recorded from the biceps brachii. The subjects completed a post-test questionnaire (PTQ) with Likert-type items to quantify the contribution of the PS (fatigue and pain of the biceps brachii, forearm muscles, and hand muscles) and PF (loss of focus and motivation) to task termination. Dependent t-tests were used to compare mean differences for normalized torque, EMG amplitude (AMP), EMG mean power frequency (MPF), MMG AMP, MMG MPF, and neuromuscular efficiency (NME = normalized TRQ / normalized EMG AMP). Spearman’s rank order correlations were used to assess the relationships among the PTQ items, time to task failure (TTF; 503.01 ± 401.1 s), and performance fatigability (% decline in MVIC; 12.4 ± 12.4%). RESULTS: There were significant (p ≤ 0.05) fatigue-induced decreases from pre-test to post-test for torque (100.0 ± 0.0 vs 87.6 ± 12.4%) and EMG AMP (100.0 ± 0.0 vs 83.9 ± 21.7%) but no significant (p > 0.05) changes for EMG MPF, MMG AMP, MMG MPF, and NME. There were significant (p ≤ 0.05, rs = 0.591 - 0.891) associations among the PTQ items, but no significant (p > 0.05, rs = -0.318 - 0.420) associations for the PTQ items versus TTF or performance fatigability. CONCLUSIONS: The fatigue-induced decrease in EMG AMP tracked the decrease in torque. Furthermore, there were intercorrelations between the PS and PF, however, none were related to TTF or performance fatigability, which suggested that other factors may have contributed to task termination, like effort, discomfort, and affective valence.