Neuromuscular And Perceived Responses Following A Fatiguing Task Anchored To A Low Torque Intensity

PURPOSE: Few studies have examined the relationships among factors associated with perceived fatigability and performance fatigability (PF). Therefore, this study examined the relationships among PF, time to task failure (TTF), neuromuscular responses, and the perceived sensations of fatigue, pain, motivation, and focus following a sustained, isometric forearm flexion fatiguing task (FT) anchored to a low torque intensity. 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 maximal voluntary isometric contractions (MVIC) prior to and following a FT to determine PF (% decline in MVIC). The FT was anchored to a target torque that corresponded to a rating of perceived exertion of 4 (35.9 ± 11.5% MVIC) and was maintained to task failure (inability to maintain the target torque despite strong verbal encouragement). Electromyographic (EMG) and mechanomyographic (MMG) signals were recorded from the biceps brachii (BB) during the MVICs. The subjects completed a post-test questionnaire (PTQ) with Likert-type items to quantify the contributions of fatigue and pain from the BB, forearm muscles (FM), and hand muscles (HM), as well as motivation and focus to the decision to terminate the task. Dependent t-tests were used to determine pre-test versus post-test mean differences for MVIC as well as normalized (to pre-test MVIC values) EMG amplitude (AMP), EMG mean power frequency (MPF), MMG AMP, MMG MPF, and neuromuscular efficiency (NME = normalized torque / normalized EMG AMP). Spearman’s rank order correlations were used to quantify the correlations between the PTQ items, TTF, and PF. RESULTS: There were significant (p < 0.05) fatigue-induced decreases from pre-test to post-test for MVIC and EMG MPF, but no significant (p > 0.05) changes for EMG AMP, MMG AMP, MMG MPF, or NME. There were significant (p < 0.05) correlations among the PTQ items, as well as FM and HM pain versus PF (rs = -0.638 and -0.605, respectfully). There were no significant (p > 0.05) correlations for the PTQ items versus TTF. CONCLUSION: The fatigue-induced decreases in EMG MPF tracked the decrease in MVIC, which suggested the presence of peripheral fatigue. Furthermore, pain in the FM and HM were the only perceived sensations that were correlated with PF.