D-24 Free Communication/Poster - Altitude and Hypoxia: MAY 28, 2009 1:00 PM - 6:00 PM ROOM: Hall 4F
Recently, high-altitude training has been used for improving the performance of athletes participating in not only endurance events but also relatively short-distance events. However, the effects of high-altitude training on muscle energy metabolism have not been clarified.
PURPOSE: This study aimed to determine the characteristics of muscle energy metabolism during exercise under conditions of acute hypoxia.
METHODS: Six subjects (age: 27-31 years) performed dynamic knee-extension exercise while lying supine on a super-conducting magnet under conditions of normoxia (FIO2 = 20.9%) and hypoxia (FIO2 = 13.0%). The workload was increased every 2 min until exhaustion. Quadriceps femoris muscle energy metabolism and oxygen kinetics were measured using 31phosphorus magnetic resonance spectroscopy (31P-MRS) and near-infrared spectroscopy (NIRS). The muscle oxygen consumption (VO2mus) was estimated by the decreasing rate of oxygenated hemoglobin during temporal arterial occlusion. The pulmonary oxygen uptake (VO2pul) was also measured by the Douglas bag method.
RESULTS: The values of muscle phosphocreatinine (PCr), muscle pH, VO2mus, and VO2pul significantly reduced at identical submaximal workloads under hypoxic conditions as compared to the corresponding values under normoxic conditions (p < 0.05). The muscle PCr at exhaustion was almost entirely depleted under both conditions, and these values did not significantly differ between the 2 conditions. However, the muscle pH, VO2mus, and VO2pul values at exhaustion were significantly lower during hypoxia than during normoxia (p < 0.05).
CONCLUSIONS: The data of muscle PCr and pH at exhaustion suggest that glycolytic system contributes to a greater extent under hypoxic conditions than normoxic conditions during high-intensity exhaustive exercise. The results of this study suggest that as compared to normoxic conditions, hypoxic conditions cause a reduction in the muscle aerobic energy supply and an increment in the anaerobic energy supply during exercise at identical workloads.