Falk B, Burstein R, Rosenblum J, Shapiro Y, Zylber-Katz E, Bashan N
Faculty of Health Sciences, McMaster University, Hamilton, Ont., Canada.
Can J Physiol Pharmacol. 1990 Jul;68(7):889-92. doi: 10.1139/y90-135.
This study investigated the effects of caffeine supplementation on thermoregulation and body fluid balance during prolonged exercise in a thermoneutral environment (25 degrees C, 50% RH). Seven trained male subjects exercised on a treadmill at an intensity of 70-75% of maximal oxygen consumption to self-determined exhaustion. Subjects exercised once after caffeine and once after placebo ingestion, given in a double-blind crossover design. Five milligrams per kilogram body weight of caffeine followed by 2.5 mg.kg-1 of caffeine were given 2 and 0.5 h before exercise, respectively. Rectal temperature was recorded and venous blood samples were withdrawn every 15 min. Water loss and sweat rate were calculated from the difference between pre- and post-exercise body weight, corrected for liquid intake. Following caffeine ingestion, when compared with placebo, no significant difference in final temperature or in percent change in plasma volume were found. No significant differences were observed in total water loss (1376 +/- 154 vs. 1141 +/- 158 mL, respectively), sweat rate (12.4 +/- 1.1 vs. 10.9 +/- 0.7 g.m-2.min-1, respectively), rise in rectal temperature (2.1 +/- 0.3 vs. 1.5 +/- 0.4 degrees C, respectively), nor in the calculated rate of heat storage during exercise (134.4 +/- 17.7 vs. 93.5 +/- 22.5 W, respectively). Thus, in spite of the expected rise in oxygen uptake, caffeine ingestion under the conditions of this study does not seem to disturb body fluid balance or affect thermoregulation during exercise performance.
本研究调查了在热中性环境（25摄氏度，相对湿度50%）下长时间运动期间补充咖啡因对体温调节和体液平衡的影响。七名受过训练的男性受试者在跑步机上以最大耗氧量的70 - 75%的强度运动至自我感觉疲劳。受试者在双盲交叉设计下，分别在摄入咖啡因和安慰剂后各进行一次运动。在运动前2小时和0.5小时分别给予每千克体重5毫克咖啡因，随后给予每千克体重2.5毫克咖啡因。记录直肠温度，并每隔15分钟采集静脉血样。根据运动前后体重的差异计算失水量和出汗率，并校正液体摄入量。与安慰剂相比，摄入咖啡因后，最终体温或血浆容量的百分比变化没有显著差异。在总失水量（分别为1376±154毫升和1141±158毫升）、出汗率（分别为12.4±1.1克·平方米·分钟⁻¹和10.9±0.7克·平方米·分钟⁻¹）、直肠温度升高（分别为2.1±0.3摄氏度和1.5±0.4摄氏度）以及运动期间计算的热量储存率（分别为134.4±17.7瓦和93.5±22.5瓦）方面均未观察到显著差异。因此，尽管预期摄氧量会增加，但在本研究条件下摄入咖啡因似乎不会干扰体液平衡或影响运动表现期间的体温调节。
