Study of the effect on oxidative metabolism, muscle composition, and metabolic cost in high altitude walking women

Aim: During Hypobaric hypoxia (Hh) the oxygen level in the bloodstream is reduced and body responses lead to physiological adaptations that determines the modulation of oxygen transport/utilization and, for more than 4 weeks exposure to Hh, changes in structural and functional properties take place. Permanence to 4000–5000 m altitude lead to muscular arrangements similar to those resulting after endurance training and the addition of physical exercise further improve aerobic performance through adaptations of muscle oxidative metabolism. Even if a sex dependent response to chronic hypoxia has been described, only few studies involving female about physiological adaptation to high-altitude are published1,2. Methods: Seven healthy women (36.3yy ± 7.1; 65.8kg ± 11.7; 165cm ± 8) were enrolled to participate in two 20-day trekking expeditions, respectively at 598 m and 4132 m of altitude, separated by 4 months of recovery. Before (B1, B2) and after (P1, P2) each expedition we measured maximal oxygen uptake, VO2 and systemic O2 delivery (QaO2) kinetics during moderate-intensity exercise and energy cost of locomotion. Furthermore, muscle structure (slow/fastMyHC isoforms), mitochondrial features and mass were analyzed from muscular biopsies obtained at B1, P1 and P2. Results: Both of altitude trekking reveal: No changes in QaO2 kinetics, faster mean response time of VO2 kinetics (P = 0.002, P = 0.001) and smaller oxygen deficit (P = 0.001, P = 0.0004). No changes in MyHC isoforms expression and mitochondrial mass. Decrease in ADP-stimulate mitochondrial respiration (P = 0.016), increase in leak respiration (P = 0.031) and in the respiratory control ratio (P = 0.016) Conclusion Training don’t affect muscle phenotype but it induced beneficial adaptations of the oxygen transport-utilization systems demonstrated by faster VO2 kinetics at exercise onset.