Sex and performance-level differences in aerobic and haematological parameters among elite ski mountaineering...

Ski mountaineering (SkiMo) is a new Olympic sport with extreme endurance demands and altitude exposure. Previous studies have focused on traditional cardiorespiratory variables, such as maximal oxygen consumption ( ${\dot{V}}_{O_2\max }$ ) or ventilatory thresholds, but, to our knowledge, did not report haemoglobin mass (Hbmass). The aim of this study was to investigate the relationship between Hbmass and ${\dot{V}}_{O_2\max }$ in elite SkiMo athletes and compare physiological differences across performance levels. Twenty-nine Swiss national team SkiMo athletes (10 females and 19 males) were classified into Tier 3-5. Participants performed a treadmill graded exercise test (25% slope) to determine ${\dot{V}}_{O_2\max }$ and ventilatory thresholds. The Hbmass and blood volumes were assessed using a CO-rebreathing technique. Sex and tier-based comparisons were made, and correlations between haematological parameters and aerobic performance metrics were analysed. The Hbmass normalized to body mass (HbmassBM) was significantly correlated with ${\dot{V}}_{O_2\max }$ in the pooled group (r = 0.80, P < 0.001), females (r = 0.82, P = 0.007) and males (r = 0.53, P = 0.024). The Hbmass and related haematological parameters were significantly higher in males (P < 0.05). Males in Tier 5 had higher oxygen consumption at the second ventilatory threshold (63.0 ± 4.3 vs. 58.9 ± 2.8 mL min^-1 kg^-1; P = 0.022) and ${\dot{V}}_{O_2\max }$ (72.0 ± 4.4 vs. 67.4 ± 3.1 mL min^-1 kg^-1; P = 0.015) than those in Tier 3-4. The significant correlation between HbmassBM and ${\dot{V}}_{O_2\max }$ confirms the key role of Hbmass in oxygen transport and aerobic capacity. However, Tier 5 athletes achieved superior aerobic performance without higher HbmassBM, indicating that additional physiological factors underpin elite-level performance.