Mechanisms of fatigue differ after low‐ and high‐force fatiguing contractions in men and women

Abstract

The magnitude of failure in voluntary drive after fatiguing contractions of different intensities in men and women is not known. The purpose of this study was to compare the time to task failure and voluntary activation of men and women for a sustained isometric contraction performed at a low and high intensity with the elbow flexor muscles. Nine men and nine women sustained an isometric contraction at 20% and 80% of maximal voluntary contraction (MVC) force until task failure during separate sessions. The men had a shorter time to failure than women for the 20% but not the 80% MVC task. Voluntary activation was reduced to similar levels for the men and women at the end of the fatiguing contractions but was reduced less after the 80% MVC task than the 20% MVC contraction. Twitch amplitude was reduced similarly at task failure for both sexes and to similar levels at termination of the 20% and 80% MVC tasks. The rate of change in mean arterial pressure was the main predictor of time to failure for the low-force sustained contraction. These results suggest that women experienced greater muscle perfusion, less peripheral fatigue, and a longer time to task failure than men during the low-force fatiguing contraction. However, the low-force task induced greater central fatigue than the high-force contraction for both men and women. Thus, low-force, long-duration fatiguing contractions can be used in rehabilitation to induce significant fatigue within the central nervous system and potentially greater neural adaptations in men and women.

Sex Differences in Arm Muscle Fatigability With Cognitive Demand in Older Adults

“…Furthermore, low-force contractions, which were sustained for longer durations than high-force tasks, involve greater fatigue originating from the central nervous system and upstream of the motor cortex, particularly in older adults [32,39,40].…”

Comparison of neuromuscular adjustments associated with sustained isometric contractions of four different muscle groups

“…We further expected that the MVC force decline immediately after task failure would be considerably less than 50% of MVC, even though the sustained contraction was performed at 50% MVC force; in other words, there would still be a reserve in muscle maximal force-generating capacity at the point of task failure. Second, as it has previously been shown that peripheral impairments were more pronounced after high-force-contraction tasks (10,50), whereas central alterations were found to increase with task duration (7,50,78), we hypothesized that, despite a similar decrease in MVC force for the different muscle groups, the relative contribution of central and peripheral mechanisms would be mainly determined by the duration of the sustained contraction.…”

Distinct profiles of neuromuscular fatigue during muscle contractions below and above the critical torque in humans

“…17,43,49 for discussion), and it can only indicate the presence of central fatigue and not its cause or location in the CNS (49). The extent to which central or peripheral mechanisms of fatigue are involved in the reduction in maximal torque-generating capacity depends on a number of factors, including contraction intensity (20,56), whether the contractions are sustained or intermittent (12), the muscle group used (10), and the age and/or sex of the subjects (26,32). In short, fatigue is task dependent (22).…”

“…Specifically, during prolonged contractions (sustained or intermittent) at a low fraction of the MVC torque (ϳ5-30% MVC), the extent of central fatigue is substantial (47,48,56) and significantly greater than that during contractions at higher fractions of the MVC (20). In contrast, when submaximal contractions are performed at relatively high intensities (greater than ϳ30% MVC), peripheral fatigue is substantial (10,25,45), and central fatigue is either modest (20,56) or absent (10). However, it is not known whether the transition in fatigue processes between low-intensity and high-intensity contractions occurs gradually as the torque requirements are increased, or whether this transition occurs suddenly at some identifiable "threshold".…”

“…These metabolic perturbations (particularly increased inorganic phosphate) have been suggested to play a key role in the development of peripheral fatigue (55). In contrast, contractions performed below ϳ30% MVC are associated with small changes in muscle metabolite concentrations (41,51) and surface EMG amplitudes (48,56). Similarly, modest changes in the muscle metabolic responses are observed during knee extensor exercise performed below critical power (33).…”