Sex differences in fatigability following exercise normalised to the power–duration relationship

Abstract

Key points Knee‐extensors demonstrate greater fatigue resistance in females compared to males during single‐limb and whole‐body exercise. For single‐limb exercise, the intensity–duration relationship is different between sexes, with females sustaining a greater relative intensity of exercise. This study established the power–duration relationship during cycling, then assessed fatigability during critical power‐matched exercise within the heavy and severe intensity domains. When critical power and the curvature constant were expressed relative to maximal ramp test power, no sex difference was observed. No sex difference in time to task failure was observed in either trial. During heavy and severe intensity cycling, females experienced lesser muscle de‐oxygenation. Following both trials, females experienced lesser reductions in knee‐extensor contractile function, and following heavy intensity exercise, females experienced less reduction in voluntary activation. These data demonstrate that whilst the relative power–duration relationship is not different between males and females, the mechanisms of fatigability during critical power‐matched exercise are mediated by sex. Abstract Due to morphological differences, females demonstrate greater fatigue resistance of locomotor muscle during single‐limb and whole‐body exercise modalities. Whilst females sustain a greater relative intensity of single‐limb, isometric exercise than males, limited investigation has been performed during whole‐body exercise. Accordingly, this study established the power–duration relationship during cycling in 18 trained participants (eight females). Subsequently, constant‐load exercise was performed at critical power (CP)‐matched intensities within the heavy and severe domains, with the mechanisms of fatigability assessed via non‐invasive neurostimulation, near‐infrared spectroscopy and pulmonary gas exchange during and following exercise. Relative CP (72 ± 5 vs. 74 ± 2% Pmax, P = 0.210) and curvature constant (51 ± 11 vs. 52 ± 10 J Pmax−1, P = 0.733) of the power–duration relationship were similar between males and females. Subsequent heavy (P = 0.758) and severe intensity (P = 0.645) exercise time to task failures were not different between sexes. However, females experienced lesser reductions in contractile function at task failure (P ≤ 0.020), and greater vastus lateralis oxygenation (P ≤ 0.039) during both trials. Reductions in voluntary activation occurred following both trials (P < 0.001), but were less in females following the heavy trial (P = 0.036). Furthermore, during the heavy intensity trial only, corticospinal excitability was reduced at the cortical (P = 0.020) and spinal (P = 0.036) levels, but these reductions were not sex‐dependent. Other than a lower respiratory exchange ratio in the heavy trial for females (P = 0.039), no gas exchange variables differed between sexes (P ≥ 0.052). Collectively, these data demonstrate that whilst the relative power–duration relationship is not different between males and females, the mechanis...

Physiological sex differences affect the integrative response to exercise: acute and chronic implications

“…Consistently in the studies by Ansdell et al. (2019a, 2020), it was demonstrated that for an equivalent duration of high‐intensity exercise, females experienced less contractile dysfunction than males, potentially indicative of less disruption to the muscle metabolic environment and, perhaps, less of an adaptive stimulus for an equivalent amount of work. Evidence from proton magnetic resonance spectroscopic techniques during isometric exercise modalities would support this notion, indicating greater acidosis (Russ et al., 2005); however, equivalent data during locomotor exercise are difficult to obtain and, as yet, it is unknown whether the same phenomenon occurs.…”

“…In two recent experiments that took the threshold normalization approach, one single‐limb (Ansdell et al., 2019a) and one cycling exercise (Ansdell et al., 2020), a consistent finding was that for the same duration and intensity of exercise, females experienced approximately half the reduction in contractile function of males in the knee extensors at the end of the fatiguing exercise (e.g. Figure 3b).…”

“…Conceivably, any sex difference in these processes could influence the excitability and function of the CNS. Evidence has shown less of a decline in VA after cycling exercise below critical power (CP) compared with above CP, despite a lack of difference in the excitability of descending tracts between males and females (Ansdell et al., 2020). However, further investigation is required into this topic; likewise, the influence of the menstrual cycle on CNS function during exercise is currently unknown.…”

Identifying sex differences in neuromuscular fatigue: the challenge of normalizing exercise intensity and interpreting the results between populations

“…As a result, males and females could experience substantial differences in time to task failure, which would be a serious limitation as the intensity and duration of the exercise task are known to influence the magnitude and aetiology of neuromuscular fatigue (Ducrocq et al 2021). In order to circumvent this limitation, Ansdell et al (2020a) normalized exercise intensity to critical power, a metabolic threshold derived from the power-time relationship, with the intention to match the metabolic rate between males and females.…”

“…However, similarly to other research areas, sex differences in neuromuscular fatigue are still under-investigated (Hunter, 2016). In a recent article published in The Journal of Physiology, Ansdell and colleagues aimed to clarify the sex differences in fatigue during whole-body exercise (Ansdell et al 2020a).…”