Linear decrease in $\dot V\hbox{O}_{2\max}$ and performance with increasing altitude in endurance athletes

Abstract

It has been hypothesized that one reason for decreased $\dot V\hbox{O}_{2\max}$ in hypoxia could be the lower maximal exercise intensity achieved in incremental, time or distance trial tests. We hypothesized that (1) $\dot V\hbox{O}_{2\max}$ would be decreased at altitude even when exercising at the same absolute maximal exercise intensity as at sea level and; (2) the decline in $\dot V\hbox{O}_{2\max}$ in endurance-trained athletes (ETA) would be linear across the range from sea level through moderate altitudes. Eight ETA performed combined $\dot V\hbox{O}_{2\max}$ 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 O₂ saturation. $\dot V\hbox{O}_{2\max}$ 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 $\dot V\hbox{O}_{2\max}$ decreased with 14.5% (P<0.001) per 1,000 m altitude between 300 and 2,800 m. Both $\dot V\hbox{O}_{2\max}$ 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 $\dot V\hbox{O}_{2\max}$ decline from 300 to 800 m above sea level and continued to decrease linearly to 2,800 m.