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

Introduction: Peak oxygen uptake (V̇O ) declines by ~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 V̇O than in endurance performance with altitude suggests a higher fractional utilization of V̇O (%V̇O ). Therefore, we hypothesized that the %V̇O 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, V̇O : 60 ± 8 mL min  kg ) 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, V̇O was determined, and during a 40-min all out maximal effort time trial (TT), mean power output (MPO) and mean V̇O (%V̇O ) were assessed.

Results: V̇O 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, %V̇O 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  kJ ) was poorer (+3.4 ± 2.7%, p < 0.001).

Conclusion: The %V̇O 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 V̇O . Future studies should address the physiological mechanisms underlying the elevated %V̇O .