Sex Differences in Maximal Oxygen Uptake Adjusted for Skeletal Muscle Mass in Amateur Endurance Athletes: A Cross Sectional Study

Male athletes tend to outperform female athletes in several endurance sports. Maximum cardiac output can be estimated by maximal oxygen consumption ([Formula: see text]), and it has been established that men present [Formula: see text] values about 20% higher than women. Although sex differences in [Formula: see text] have already been well studied, few studies have assessed sex differences with regard to muscle oxidative capacity. The aim of this study was to compare aerobic muscle quality, accessed by [Formula: see text] and adjusted by lower limb lean mass, between male and female amateur triathletes. The study also aimed to compare sex differences according to [Formula: see text] submaximal values assessed at ventilatory thresholds. A total of 57 participants (23 women and 34 men), who had been training for Olympic-distance triathlon races, underwent body composition evaluation by dual-energy X-ray absorptiometry and performed a cardiorespiratory maximal test on a treadmill. Male athletes had significantly higher [Formula: see text] , both absolutely and when adjusted to body mass. Conversely, when [Formula: see text] was adjusted for lean mass, there was no significant difference between sexes. The same was observed at submaximal exercise intensities. In conclusion, differences in [Formula: see text] adjusted to body mass but not lean mass may explain, at least in part, sex differences in performance in triathlons, marathons, cycling, and other endurance sports.