INTRODUCTION: Ski mountaineering (SkiMo) will be an Olympic sport (i.e., sprint and mixed relay events) at the upcoming 2026 Winter Olympic games. Despite its rising prominence, there is surprisingly a lack of research on SkiMo compared to the other winter sports [1]. SkiMo sprint is extremely demanding, uphill exercise time being ~80-93% of total race time in elite athletes [2]. Consequently, both body composition and maximal oxygen consumption (VO2max) are paramount [3]. Previous studies have reported the physiological characteristics of elite male SkiMo athletes but limited data exist on female athletes [3,4]. To address this gap, the present study aimed to analyze sex differences in physiological parameters of elite SkiMo athletes. The hypothesis was that sex differences in vertical velocity (vV) would exceed the differences in VO2 at submaximal and maximal aerobic intensities. METHODS: Twenty elite ski mountaineers (6 women, 14 men), member of the Swiss national team, aged 20-32 years, participated in this study. They all had competed at the World Cup level, with many achieving top-3 ranking. Athletes performed a submaximal exercise followed by a graded exercise to exhaustion (treadmill with 25% slope; initial speed = 3.5 km/h for women and 4 km/h for men; increment = 0.3 km/h each 1-min stage; with poles) with breath-by-breath cardiorespiratory measurements continuously collected (Quark CPET, Cosmed, Rome, Italy). The first and second ventilatory thresholds (VT1, VT2), as well as at maximal intensity (MAX), were determined by visual inspection from three examiners. RESULTS/DISCUSSION: Elite female SkiMo athletes had a VO2 value 13.6% lower at MAX (64.0 ± 3.8 vs. 72.8 ± 5.5 ml/kg/min; p = 0.002) and 15.5% lower at VT2 (54.8 ± 2.8 vs. 62.2 ± 5.8 ml/kg/min; p = 0.009) than their male counterparts. Interestingly, the sex-differences in vV at both MAX (1825 ± 113 vs. 2125 ± 156 m/h; p < 0.001; 16.4%). and VT2 (1412 ± 56 vs. 1696 ± 151 m/h; p < 0.001; 20.1%) intensities were consistently larger than the differences in VO2, which supports the main hypothesis. Further investigation on the underlying mechanisms is requested but the following factors may contribute to the larger sex-differences in uphill velocity than in the well-known aerobic power [5]: Firstly, women generally have a higher body fat percentage, a finding corroborated in our study (15.2 ± 1.0% vs. 6.6 ± 0.6%; p = 0.004). Secondly, women have a higher proportion of slow-twitch oxidative fibers and fewer fast-twitch fibers, which may disadvantage them in uphill locomotion due to its reliance on concentric contractions and force production. Additionally, men also generate more power output, likely due to greater upper body muscle mass [6]. Finally, the pulmonary system shows significant sex differences during hypoxia, with women experiencing greater hypoxemia and increased work of breathing compared to men [7]. CONCLUSION: The sex-differences in uphill velocities (16.4-20.1%) were larger than the differences in VO2 (13.6-15.5%) or than the commonly reported 10-12% difference in road runners [8]. Overall, the present findings are in line with the 16-17% difference in performance times reported in three major mountain ultra-marathons [9]. The performance gaps between men and women appear to be larger in uphill sports.
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