(6) SIMILAR RESPONSES TO FATIGUE IN MEN AND WOMEN FOLLOWING SUSTAINED, ISOMETRIC FOREARM FLEXION TASKS ANCHORED TO RPE AND TORQUE

Few studies have simultaneously assessed the amplitude (AMP) and mean power frequency (MPF) of electromyographic (EMG) and mechanomyographic (MMG) signals during tasks anchored to a rating of perceived exertion (RPE) and torque to compare the changes in the neuromuscular and mechanical properties of muscle function.

Purpose: The purpose of this study was to examine the effects of anchor scheme and sex on maximal voluntary isometric contraction (MVIC) torque, EMG, and MMG responses following sustained, isometric forearm flexion tasks in men and women.

Methods: Fourteen recreationally active adults (7 men and 7 women) performed 2, 3s forearm flexion MVICs before and after sustained, isometric forearm flexion tasks to failure (elbow joint angle = 100°) anchored to RPE = 7 (RPEFT) and the initial torque (TRQFT) that corresponded to RPE = 7. Task failure for the RPEFT was defined as RPE > 7, or torque reduced to zero. For the TRQFT, task failure was defined as the inability to maintain the target torque value. During testing, torque was recorded on a Cybex 6000 dynamometer, with the EMG and MMG signals recorded from the biceps brachii (BB). Five, separate 2 (Time: Pretest vs. Posttest) × 2 (Anchor Scheme: RPEFT vs. TRQFT) × 2 (Sex: Men vs. Women) mixed factorial ANOVAs were performed for torque and the neuromuscular parameters (EMG AMP, EMG MPF, MMG AMP, and MMG MPF). Bonferroni corrected post-hoc dependent t-tests and independent t-tests were used when necessary.

Results: Post-hoc comparisons indicated a decrease in torque (collapsed across sex) from pretest to posttest MVICs (45.9 ± 5.6 vs. 40.9 ± 5.9 Nm; p < 0.001) and that the men produced a greater MVIC than the women (58.5 ± 6.4 vs. 28.3 ± 9.8 Nm; p < 0.001). Furthermore, post-hoc comparisons indicated a decrease in EMG AMP (collapsed across sex) from pretest to posttest MVICs (720.3 ± 136.6 vs. 603.2 ± 123.0 µVrms; p = 0.003) and that the men had a greater MMG AMP than the women (0.72 ± 0.14 vs. 0.60 ± 0.12 m∙s^-2). There were no changes for EMG MPF or MMG MPF.

Conclusions: The present findings were consistent with the typical sex-specific differences in MVIC torque production during upper body tasks. Our findings indicated, however, that men and women exhibited similar fatigue-induced decreases in MVIC, regardless of anchor scheme. It is possible, that the fatigue-induced decreases in EMG AMP indicated a decrease in muscle excitation associated with reductions in central command due to peripheral factors that caused central fatigue and likely contributed to fatigue-induced decreases in MVIC. In addition, it may be that the men relied more on motor unit recruitment (based on MMG AMP) during the MVICs than the women, which suggested there may be sex-specific differences in motor unit activation strategies involved with the production of MVIC torque values during forearm flexion tasks. PRACTICAL APPLICATIONS: EMG and MMG can be used to examine both the neuromuscular and mechanical aspects of muscle function following fatiguing tasks utilizing different anchor schemes to provide information about the mechanisms of fatigue-induced changes in muscular strength for men and women.

Acknowledgements: None.