Abstract
Females have lower fatigability than males during single limb isometric and dynamic contractions, but whether sex-differences exist during high-intensity whole-body exercise remains unknown. This study shows that males and females respond similarly to repeated supramaximal whole-body exercise, and that at task failure a large functional reserve remains in both sexes. Using post-exercise ischaemia with repeated exercise, we have shown that this functional reserve depends on the glycolytic component of substrate-level phosphorylation and is almost identical in both sexes. Metaboreflex activation during post-exercise ischaemia and the O2 debt per kg of active lean mass are also similar in males and females after supramaximal exercise. Females have a greater capacity to extract oxygen during repeated supramaximal exercise and reach lower , experiencing a larger drop in brain oxygenation than males, without apparent negative repercussion on performance. Females had no faster recovery of performance after accounting for sex differences in lean mass. The purpose of this study was to ascertain what mechanisms explain sex differences at task failure and to determine whether males and females have a functional reserve at exhaustion. Exercise performance, cardiorespiratory variables, oxygen deficit, and brain and muscle oxygenation were determined in 18males and 18 females (21-36years old) in two sessions consisting of three bouts of constant-power exercise at 120% of until exhaustion interspaced by 20s recovery periods. In one of the two sessions, the circulation of both legs was occluded instantaneously (300mmHg) during the recovery periods. Females had a higher muscle O2 extraction during fatiguing supramaximal exercise than males. Metaboreflex activation, and lean mass-adjusted O2 deficit and debt were similar in males and females. Compared to males, females reached lower and brain oxygenation during supramaximal exercise, without apparent negative consequences on performance. After the occlusions, males and females were able to restart exercising at 120% of , revealing a similar functional reserve, which depends on glycolytic component of substrate-level phosphorylation and its rate of utilization. After ischaemia, muscle O2 extraction was increased, and muscle was similarly reduced in males and females. The physiological response to repeated supramaximal exercise to exhaustion is remarkably similar in males and females when differences in lean mass are considered. Both sexes fatigue with a large functional reserve, which depends on the glycolytic energy supply, yet females have higher oxygen extraction capacity, but reduced and brain oxygenation.
Highlights
During whole-body high-intensity exercise to exhaustion, it is likely that task failure occurs due to a higher energy demand than energy supply
The main finding of the present investigation is the demonstration that males and females respond to repeated supramaximal whole-body exercise to exhaustion and that at task failure a large functional reserve remains in both sexes
Males and females performed the exercise at an intensity which should have exhausted the anaerobic capacity (Medbo & Tabata, 1993; Gastin et al 1995; Calbet et al 1997), a similar functional reserve in substrate-level phosphorylation energy supply per kg of lower extremities lean mass was observed at task failure in both sexes
Summary
During whole-body high-intensity exercise to exhaustion, it is likely that task failure occurs due to a higher energy demand than energy supply. We define ‘functional reserve’ as the capacity to produce power at the same level or higher than reached at exhaustion This functional reserve has been demonstrated in males by the capacity to perform sprint exercise at the end of an incremental exercise test to exhaustion followed by 10–60 s ischaemia, which impedes metabolic recovery (Morales-Alamo et al 2015; Gelabert-Rebato et al 2018, 2019a,b) as well as after 3–5 s recovery without occlusion (Coelho et al 2015). The physiological factors determining the nature and magnitude of the functional reserve and whether sex differences exist have not been established
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