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

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.