No abstract

During exercise, healthy individuals are able to maintain arterial oxygenation, whereas highly-trained endurance athletes may exhibit an exercise-induced arterial hypoxaemia (EIAH) that seems to reflect a gas exchange abnormality. The effects of EIAH are currently debated, and different hypotheses have been proposed to explain its pathophysiology. For moderate exercise, it appears that a relative hypoventilation induced by endurance training is involved. For high-intensity exercise, ventilation/perfusion (V(A)/Q) mismatching and/or diffusion limitation are thought to occur. The causes of this diffusion limitation are still under debate, with hypotheses being capillary blood volume changes and interstitial pulmonary oedema. Moreover, histamine is released during exercise in individuals exhibiting EIAH, and questions persist as to its relationship with EIAH and its contribution to interstitial pulmonary oedema. Further investigations are needed to better understand the mechanisms involved and to determine the long term consequences of repetitive hypoxaemia in highly trained endurance athletes.

The aim of this study was to quantify and describe the exercise intensity of ski mountaineering racing, and to identify the best physiological predictors of ski mountaineering racing. Before participating in the race in which heart rate (HR) and speed were continuously recorded, 10 trained ski-mountaineers performed a field maximal test to determine the first ventilatory threshold (VT1) and the respiratory compensation threshold (RCT) in order to establish 3 exercise intensity zones (Z1: below VT1, Z2: between VT1 and RCT, and Z3: above RCT). Energy cost (EC) of each subject was estimated on the HR/ V˙O2 relationship obtained during the field maximal test. VT1 and RCT threshold were equal to 84.2±3.0 and 94.5±1.7% of HR (max). Race time was significantly correlated with V˙O2max (r = -0.87), VT1 (r = -0.82) and RCT (r = -0.85) expressed for body mass unit. The mean race time and the mean HR were 101±11 min and 93.4±1.8% of HR (max). The % race time spent in Z1, Z2 and Z3, were 7.0±4.8, 51.3±4.7 and 42.0±6.5%, respectively. The mean value of EC during the two uphill of the race was 14.3±2.6 J x kg(-1) x m(-1). HR and speed decreased significantly during the second uphill whereas EC increased significantly by ∼15%. Data obtained in the present study represent the first qualitative description of physiology demand of ski mountaineering racing. The long period of time spent just below and above RCT suggest that ski-mountaineering can be viewed as one of the most strenuous endurance sports like cross-country skiing, running and off-road biking. In addition to high aerobic capacities, body mass seems to appear as a key factor given that performance in ski mountaineering is strongly correlated to relative common physiological variables. The changes of HR, speed and EC during the second uphill, which indicate the prevalence of fatigue, confirm the exhaustive character of ski mountaineering.

When oxygen uptake measured at the VT was expressed as a percentage of V02 max, the values obtained were also significantly higher. The increased values of Tfr and sTfr/serum proteins, respectively, above 10 microg x mL(-1) and 153, indicated the probable intake of rHuEpo.