Substrate utilization during exercise and recovery at moderate altitude

Recent studies have shown that exercise training at moderate altitude or in moderate hypoxia improved glycemic parameters. From these data, it has been supposed that endurance exercise in moderate hypoxia affects substrate utilization and that exposure to moderate hypoxia in combination with exercise may be utilized as part of metabolic or diabetes prevention program. However, the influence of exercise at moderate hypoxia on circulating metabolites and hormones in terms of substrate utilization is unclear. The purpose of this study was to elucidate the influence of exercise in moderate hypoxia on substrate utilization. We determined cardiorespiratory, metabolic, and hormonal parameters during exercise and postexercise recovery at a simulated moderate altitude of 2000 m, and then we compared these variables with values obtained at sea level. Seven men participated in this study; subjects reported to the laboratory on 4 occasions. Two maximal exercise tests were performed to estimate peak oxygen uptake at the simulated 2000-m altitude and sea level on different days. Afterward, submaximal exercise tests were carried out at a simulated altitude of 2000 m or sea level, separated by 1 week. Subjects performed submaximal exercise at the same relative exercise intensity (50% peak oxygen uptake) at a simulated altitude of 2000 m and at sea level for 30 minutes. The tests were performed in random order, and subjects were blinded to the respective altitudes. Venous blood samples and expired gases were obtained before, during exercise (15 and 30 minutes), and during postexercise recovery periods (15, 30, 45, and 60 minutes). The respiratory exchange ratio during exercise and recovery at moderate altitude was greater than at sea level. The epinephrine and norepinephrine concentrations during exercise and recovery were higher (P < .05) at moderate altitude than at sea level. Free fatty acids and glycerol concentrations during recovery were lower (P < .05) at moderate altitude than at sea level. These results suggest that carbohydrate utilization is increased during exercise and postexercise recovery period in moderate hypoxia as compared with normoxia. It is also suggested that moderate hypoxia influences the changes in circulating metabolites and hormones in terms of substrate metabolism during exercise and the recovery.