Impact of living and training at low altitude for several years on endurance performance at higher altitude: Myth or...

The physiological adaptations of long-term high-altitude residents without high-altitude genetic ancestry remain poorly characterized. This study investigated whether permanent residence at low altitude (1200 m) influences performance at higher altitude (2500 m). We compared exercise responses at 2500 m in endurance-trained athletes living for several years at 1200 m versus those residing at sea level. Twenty-five male endurance athletes [13 altitude residents (AR) and 12 sea-level residents (SLR)] performed maximal incremental cycle ergometer tests in their habitual environment (BASE: 1200 m or sea level) and in simulated moderate altitude (2500 m, inspired $P_{O_2}$  = 109 mmHg). Gas-exchange, heart rate, oxygen saturation, ventilatory and performance outcomes were measured continuously. At BASE, no between-group differences were observed in anthropometrics, spirometry or aerobic capacity, while ventilatory reserve was more reduced in the AR group (P = 0.004). Both groups exhibited significant reductions in aerobic capacity, maximal oxygen saturation and peak power output at 2500 m compared with BASE. However, AR athletes exhibited a lower percentage drop in maximal oxygen saturation (P < 0.001) and aerobic capacity (P = 0.027). Maximal heart rate decreased significantly in SLR but remained unchanged in AR. At rest, the 2500 m condition significantly reduced oxygen saturation in SLR (P < 0.001) but not in AR. In conclusion, long-term residence and training at 1200 m attenuate hypoxia-induced performance decrements at 2500 m, mainly through better preservation of arterial oxygen saturation. Chronic exposure to low altitude might therefore induce functional pulmonary adaptations, with practical implications for endurance athletes training or competing at moderate altitude.