(8) Effects of a Sustained Task Anchored to a Low Perceptual Intensity on Performance Fatigability, Perceived Fatigability, and Neuromuscular Responses

Background: Performance fatigability (PF) and perceived fatigability are two interdependent attributes of fatigue defined as a decline in an objective measure of performance and the changes in sensations and perceptions associated with performance, respectively. Few studies have examined the torque (TRQ) and neuromuscular responses during a sustained, isometric forearm flexion task (SIFFT) anchored to a low rating of perceived exertion (RPE) and whether perceived sensations (PercSens) and psychological factors (PsychFact) influence the decision to terminate the task.

Purpose: This study examined the composite patterns of responses (CPoR) for TRQ, electromyographic amplitude (EMG AMP), and neuromuscular efficiency (NME=normalized TRQ/normalized EMG AMP) during a SIFFT anchored to a low RPE as well as the PercSens and PsychFact that contributed to task termination (TT).

Methods: Twelve men (mean±SD: age=20.9±2.2 yrs.; hheight= 79.8±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 (i.e., TRQ reduced to zero) anchored to RPE=2 to determine PF (% decline in MVIC). The EMG AMP was recorded from the biceps brachii (BB). Following the SIFFT, the subjects completed a post-test questionnaire (PTQ) to quantify the contribution of the PercSens (i.e., fatigue and pain of the BB, forearm muscles [FM], and hand muscles [HM]) and PsychFact (i.e., loss of focus [LOF] and motivation) to TT. The PTQ included 10 Likert-type items: (1) BB fatigue; (2) BB pain; (3) FM fatigue; (4) FM pain; (5) HM fatigue; (6) HM pain; (7) LOF; (8) Motivation 1 [Mot1: subject expended maximal effort]; (9) Motivation 2 [Mot2: subject perceived that the task could not be accomplished]; and (10) Motivation 3 [Mot3: subject became bored]. Polynomial regression analyses (linear and quadratic) were used to define the composite relationships for normalized TRQ, EMG AMP, and NME versus time (every 10%) during the SIFFT. Spearman’s Rank Order Correlations (SROC) were used to assess the relationships among the PTQ items, time to task failure (TTF; 306.9±486.4 s), and PF (7.2±11.0%).

Results: The CPoR indicated significant (p≤0.05, r=-0.776-0.976) linear decreases for TRQ, EMG AMP, and NME. The SROC indicated significant (p≤0.05, r_S=0.585-0.942) associations for BB fatigue vs. BB pain, BB fatigue vs. FM fatigue, BB fatigue vs. HM fatigue, BB pain vs. FM pain, BB pain vs. HM fatigue, BB pain vs. HM pain, FM fatigue vs. FM pain, FM fatigue vs. HM fatigue, FM fatigue vs. HM pain, FM pain vs. HM fatigue, FM pain vs. HM pain, HM fatigue vs. HM pain, LOF vs. Mot2, LOF vs. Mot3, and Mot2 vs. Mot3. There were no significant (p>0.05, r_S=-0.263-0.458) associations for the PercSens and PsychFact items versus TTF or PF.

Conclusions: The decreases in TRQ and EMG AMP were likely associated with the ability to reduce TRQ to maintain the prescribed RPE. Furthermore, the decrease in NME, which resulted from the disproportionate fatigue-induced decrease in TRQ relative to EMG AMP, suggested the presence of peripheral mechanisms of fatigue. In addition, the PercSens were related to PsychFact, however, neither were related to TTF or PF.

Practical Applications: Practitioners may program exercises anchored to RPE as an alternative to percentages of MVIC or 1 repetition maximum loads to assess an individual’s fatigue characteristics and use PTQs to examine the contribution of PercSens and PsychFact to TT.

Acknowledgements: None.