Abstract
Background: Altitude exposure reduces maximal oxygen uptake (VO2max). Usually, the reduction is not restored with acclimatization (at least at altitudes above 2,500 m) and is more pronounced in highly trained athletes compared to nonathletes. It still remains to be elucidated whether these also apply for well-acclimatized individuals (i.e., mountain guides) acutely exposed to moderate altitude (i.e., 2,000 m). Methods: A total of 128 acclimatized male mountain guides of the Austrian armed forces (42.2 ± 7.0 years, 177.8 ± 5.6 cm, 77.2 ± 7.0 kg) of different fitness levels performed 2 incremental cycle ergometer tests 1 week apart, one at low (600 m) and one at moderate altitude (2,000 m). Oxygen uptake, heart rate (HR), and lactate concentration were measured during the tests. Results: In acclimatized mountain guides, lower baseline VO2max levels were associated with better preservation of VO2max at moderate altitude compared to higher levels. At moderate altitude, physiological responses (HR and blood lactate at 100 W) at a submaximal exercise intensity of 100 W remained unchanged or were even slightly reduced in both groups. Conclusions: Long-term acclimatization to moderate altitude may prevent the VO2max decline at a moderate altitude of 2,000 m particularly in subjects with lower VO2max levels, that is, below the 80th percentile (for age and sex). In people with higher fitness levels, VO2max may still be negatively affected. These results are of practical relevance, for example, for workers, athletes, ski and mountain guides, military staff, or rescue staff who regularly or continuously have to perform at moderate altitude.