Physiological characteristics of elite high altitude climbers

Factors underlying the amplitude of exercise performance reduction at altitude and the development of high-altitude illnesses are incompletely understood. To better describe these mechanisms, we assessed cardiorespiratory and tissue oxygenation responses to hypoxia in elite high altitude climbers. Eleven high-altitude climbers were matched with eleven non-climber trained controls according to gender, age and fitness level (maximal oxygen consumption, VO2max). Subjects performed two maximal incremental cycling tests, in normoxia and in hypoxia (inspiratory oxygen fraction: 0.12). Cardiorespiratory measurements and tissue (cerebral and muscle) oxygenation were assessed continuously. Hypoxic ventilatory and cardiac responses were determined at rest and during exercise; hypercapnic ventilatory response was determined at rest. During maximal exercise in hypoxia, climbers exhibited similar reductions than controls in VO2max (climbers -39±7%, controls -39±9%), maximal power output (climbers -27±5%, controls -26±4%) and SpO2. However, climbers had lower hypoxic ventilatory response during exercise (climbers 1.7±0.5, controls 2.6±0.7 L·min-1·%-1; p<0.05) and lower hypercapnic ventilatory response (climbers 1.8±1.4, controls 3.8±2.5 mL·min-1·mmHg-1; p<0.05). Finally, climbers exhibited slower breathing frequency, larger tidal volume and larger muscle oxygenation index. These results suggest that elite climbers show some specific ventilatory and muscular responses to hypoxia that might confer advantages for climbing at high altitude.