Dohm G L, Beeker R T, Israel R G, Tapscott E B
J Appl Physiol (1985). 1986 Oct;61(4):1363-8. doi: 10.1152/jappl.1986.61.4.1363.
Fasting before exercise increases fat utilization and lowers the rate of muscle glycogen depletion. Since a 24-h fast also depletes liver glycogen, we were interested in blood glucose homeostasis during exercise after fasting. An experiment was conducted with human subjects to determine the effect of fasting on blood metabolite concentrations during exercise. Nine male subjects ran (70% maximum O2 consumption) two counterbalanced trials, once fed and once after a 23-h fast. Plasma glucose was elevated by exercise in the fasted trial but there was no difference between fed and fasted during exercise. Lactate was significantly higher (P less than 0.05) in fasted than fed throughout the exercise bout. Fat mobilization and utilization appeared to be greater in the fasted trial as evidenced by higher plasma concentrations of free fatty acids, glycerol, and beta-hydroxybutyrate as well as lower respiratory exchange ratio in the fasted trial during the first 30 min of exercise. These results demonstrate that in humans blood glucose concentration is maintained at normal levels during exercise after fasting despite the depletion of liver glycogen. Homeostasis is probably maintained as a result of increased gluconeogenesis and decreased utilization of glucose in the muscle as a result of lowered pyruvate dehydrogenase activity.
运动前禁食可提高脂肪利用率并降低肌肉糖原消耗速率。由于24小时禁食也会消耗肝糖原，因此我们对禁食后运动期间的血糖稳态感兴趣。我们对人类受试者进行了一项实验，以确定禁食对运动期间血液代谢物浓度的影响。九名男性受试者进行了两次反向平衡试验，一次是进食后，一次是禁食23小时后，以70%的最大耗氧量进行跑步。在禁食试验中，运动使血浆葡萄糖升高，但运动期间进食组和禁食组之间没有差异。在整个运动过程中，禁食组的乳酸水平显著高于进食组（P<0.05）。禁食试验中的脂肪动员和利用率似乎更高，这表现为运动前30分钟内禁食组的游离脂肪酸、甘油和β-羟基丁酸的血浆浓度更高，以及呼吸交换率更低。这些结果表明，在人类中，尽管肝糖原耗尽，但禁食后运动期间血糖浓度仍维持在正常水平。稳态可能是由于糖异生增加以及肌肉中丙酮酸脱氢酶活性降低导致葡萄糖利用率下降而得以维持。
