The decrease in maximal oxygen consumption (VO2max) with increasing altitude has been widely investigated. The alteration in aerobic performance is significant from 800m above sea level. The percent decrease in VO2max is around 20 % at 4000m and reaches 75% at the summit of Mount Everest (8848m). It is similar in men and women. It is more pronounced in aerobically trained than sedentary subjects. This paradoxical greater impairment of aerobic performance in endurance athletes is primarily due to a greater decrease in arterial oxygen saturation at exercise in hypoxia in athletes. In men, numerous studies have reported that the drop of aerobic performance in acute hypoxia was greater in endurance athletes than in sedentary subjects. A recent study showed that it was also the case in women from an altitude of 2500m. As it is the case for men, this study reported that this difference between the two groups of female was due to a greater decrement in arterial O2 saturation (SaO2) in endurance athletes at maximal exercise. In hypoxia, the great arterial desaturation in athletes could be mainly explained by a diffusion limitation linked to a high maximal cardiac output (Qmax). Indeed, an important Qmax reduces the blood transit time in the pulmonary capillary and thus the O2 equilibrium process. As a consequence, the larger SaO2 decrease in athlete leads to a greater decrease in arterial O2 content (CaO2) and in maximal O2 transport (TO2max) and therefore the O2 available for muscles. However, in severe acute hypoxia (5300m), although two-thirds of VO2max decrease is accounted for by CaO2 reduction and one-third by the decrease in peak cardiac output and muscle blood flow. In moderate acute hypoxia, there is no consensus about Qmax changes since it was found decreased or unchanged, even though no study has focused on women exclusively so far. With regard to the important HRmax decrease, especially in trained women, a reduction in maximal cardiac output is a possible hypothesis. In this condition, a reduction in Qmax could also partly explain the VO2max decrement. Moreover, tissue O2 extraction could also be a determinant factor of VO2max in normoxia and in hypoxia. A recent theoretical study indicated that under normoxia and moderate hypoxia, limitations in both convective and diffusive O2 transport to the tissues were important factors of VO2max. Furthermore, the important difference between trained and untrained women in TO2max and tissue O2 extraction, reported as the two limiting factors of VO2max at sea level may be differently affected by hypoxia. The purpose of this study was to evaluate maximal cardiac output and O2 transport parameters in moderate acute hypoxia (1000m to 4500m) in trained and sedentary men and women in order to determine the limiting factor(s) of aerobic performance in these conditions. The use of Near infrared spectroscopy may help in evaluating tissue oxygenation. Mathematical modeling of the oxygen transport system, especially taking into account the dynamic processes involved in a progressive stepwise maximal exercise, is essential to better understand the factors involved in the decrease in aerobic performance in hypoxia and the influence of the prior training status upon this decrease.
© Copyright 2007 12th Annual Congress of the European College of Sport Science, Jyväskylä, Finland - July 11-14th 2007. Veröffentlicht von University of Jyväskylä. Alle Rechte vorbehalten.