Changes in cycling economy and fractional utilization of VO2peak during a 40-min maximal effort exercise test with acute hypobaric hypoxia corresponding to 2800 m of altitude

Introduction: Peak oxygen uptake (VO2peak) declines by similar to 7% per 1000 m of increasing altitude, whereas exercise performance seems reduced to a lesser extent. For example, 800-10 000 m track and field performances are decreased by 0.4%-2.4% above 1000 m as compared to below and some studies show similar drops in cycling performance. A greater decline in VO2peak than in endurance performance with altitude suggests a higher fractional utilization of VO2peak (%VO2peak). Therefore, we hypothesized that the %VO2peak is higher with acute hypoxic exposure than near sea level. Methods: Sixteen lowlanders (8 women, age: 31 +/- 7 years [mean +/- SD], body mass: 68 +/- 8 kg, VO2peak: 60 +/- 8 mL min(-1) kg(-1)) underwent cycling testing in a hypobaric hypoxic chamber on 6 test days, three conducted at 300 m and three at 2800 m of acute altitude. At both altitudes, VO2peak was determined, and during a 40-min all out maximal effort time trial (TT), mean power output (MPO) and mean VO2 (%VO2peak) were assessed. Results: VO2peak decreased by 11.2 +/- 3.0% (p < 0.001), while MPO during the TT declined by 10.7 +/- 3.1% (p < 0.001) at 2800 m as compared to 300 m. During the TT, %VO2peak was higher at altitude, corresponding to 75.9 +/- 4.5% at 300 m and 78.8 +/- 4.2% at 2800 m (p = 0.011), and cycling economy (mL O-2 kJ(-1)) was poorer (+3.4 +/- 2.7%, p < 0.001). Conclusion: The %VO2peak was higher during a cycling TT at 2800 m of altitude than near sea level, while cycling economy was poorer. This resulted in a similar reduction in performance and VO2peak. Future studies should address the physiological mechanisms underlying the elevated %VO2peak.