Linear decrease in VO2max and performance with increasing altitude in endurance athletes

It has been hypothesized that one reason for decreased <(V)over dot > O-2max in hypoxia could be the lower maximal exercise intensity achieved in incremental, time or distance trial tests. We hypothesized that (1) <(V)over dot > O-2max would be decreased at altitude even when exercising at the same absolute maximal exercise intensity as at sea level and; (2) the decline in <(V)over dot > O-2max in endurance-trained athletes (ETA) would be linear across the range from sea level through moderate altitudes. Eight ETA performed combined <(V)over dot > O-2max and performance tests running to exhaustion at the same speed in a randomized double blind fashion at simulated altitudes of 300, 800, 1,300, 1,800, 2,300 and 2,800 m above sea level using a hypobaric chamber. Douglas bag system was used for respiratory measurements and pulse oximetry was used to estimate arterial O-2 saturation. <(V)over dot > O-2max declined linearly from 66 +/- 1.6 ml kg(-1) min(-1) at 300 m to 55 +/- 1.6 ml kg(-1) min(-1) at 2,800 m corresponding to a 6.3% decrease per 1,000 m increasing altitude (range 4.6-7.5%). Time to exhaustion (performance) at a constant velocity associated with 107% of sea level <(V)over dot > O-2max decreased with 14.5% (P < 0.001) per 1,000 m altitude between 300 and 2,800 m. Both <(V)over dot > O-2max and performance decreased from 300 to 800 m (P < 0.01; P < 0.05). Arterial haemoglobin oxygen saturation at test cessation (SpO(2min)) declined from 89.0 +/- 2.9% at 300 m to 76.5 +/- 4.0% at 2,800 m (P = 0.001). This study report that in ETA during acute exposure to altitude both performance and <(V)over dot > O-2max decline from 300 to 800 m above sea level and continued to decrease linearly to 2,800 m.