Enhanced muscular oxygen extraction in athletes exaggerates hypoxemia during exercise in hypoxia
High rate of muscular oxygen utilization facilitates the development of hypoxemia during exercise at altitude. Because endurance training stimulates oxygen extraction capacity, we investigated whether endurance athletes are at higher risk to developing hypoxemia and thereby acute mountain sickness (AMS) symptoms during exercise at simulated high altitude. Elite athletes (ATL, n=8) and fit controls (CON, n=7) cycled for 20 min @100 Watt (EX100w) as well as performed an incremental VO2max test (EXMAX) in normobaric hypoxia (0.107 FIO2) or normoxia (0.209 FIO2). Cardiorespiratory responses, arterial PO2 (PaO2), and oxygenation status in m. vastus lateralis (TOIM) and frontal cortex (TOIC) by near-infrared spectroscopy, were measured. Muscle O2-uptake rate was estimated from Δ[O2Hb] during a 10-min arterial occlusion in m. gastrocnemius. VO2max in normoxia was 70±2 ml.min-1.kg-1 in ATL versus 43±2 in CON, and in hypoxia decreased more in ATL (- 41%) than in CON (-25%, p<0.05). Both in normoxia at PaO2 of ~95 mmHg, and in hypoxia at PaO2 of ~35 mmHg, muscle O2-uptake was 2-fold higher in ATL than in CON (0.12 vs. 0.06 ml.min-1.100g-1; p<0.05). During EX100W in hypoxia PaO2 dropped to lower (p<0.05) values in ATL (27.6±0.7 mmHg) than in CON (33.5±1.0 mmHg). During EXMAX, but not during EX100W, TOIM was ~15% lower in ATL than in CON (p<0.05). TOIC was similar between the groups at any time. This study shows that maintenance of high muscular oxygen extraction rate at very low circulating PaO2 stimulates the development of hypoxemia during submaximal exercise in hypoxia in endurance-trained individuals. This effect may predispose to premature development of AMS symptoms during exercise at altitude.
Autor / Fonte:Ruud Van Thienen, Peter Hespel Journal of Applied Physiology Published 25 November 2015 Vol. no. , DOI: 10.1152/japplphysiol.00210.2015