Graham T E, Sathasivam P, MacNaughton K W
School of Human Biology, University of Guelph, Ontario, Canada.
J Appl Physiol (1985). 1991 May;70(5):2052-8. doi: 10.1152/jappl.1991.70.5.2052.
Recently we found that caffeine ingestion did not enhance either thermal or fat metabolic responses to resting in cold air, despite an increase in plasma epinephrine and free fatty acids. Theophylline, another methylxanthine, has been shown to be effective during exercise but not at rest during cold stress. Therefore we hypothesized that caffeine ingestion before exercise in cold air would have a thermal-metabolic impact by increasing fat metabolism and increasing oxygen consumption. Young adult men (n = 6) who did not normally have caffeine in their diet performed four double-blind trials. Thirty minutes after ingesting placebo (dextrose, 5 mg/kg) or caffeine (5 mg/kg) they either exercised (60 W) or rested for 2 h in 5 degrees C air. Cold increased (P less than 0.05) plasma norepinephrine while both caffeine and exercise increased (P less than 0.05) epinephrine. Serum free fatty acids and glycerol were increased, but there were no differences between rest and exercise or placebo and caffeine. Caffeine had no influence on either respiratory exchange ratio or oxygen consumption either at rest or during exercise. The exercise trials did not significantly warm the body, and they resulted in higher plasma norepinephrine concentrations and lower mean skin temperatures for the first 30 min. The data suggest that skin temperature stimulates plasma norepinephrine while caffeine has little effect. In contrast, caffeine and exercise stimulate plasma epinephrine while cold has minimal effect. Within the limits of this study caffeine gave no thermal or metabolic advantage during a cold stress.
最近我们发现，尽管血浆肾上腺素和游离脂肪酸增加，但摄入咖啡因并不能增强在冷空气中静息时的热代谢或脂肪代谢反应。另一种甲基黄嘌呤——茶碱，已被证明在运动期间有效，但在冷应激静息时无效。因此，我们假设在冷空气中运动前摄入咖啡因会通过增加脂肪代谢和耗氧量产生热代谢影响。平时饮食中不常摄入咖啡因的年轻成年男性（n = 6）进行了四项双盲试验。在摄入安慰剂（葡萄糖，5 mg/kg）或咖啡因（5 mg/kg）30分钟后，他们要么进行运动（60 W），要么在5摄氏度的空气中静息2小时。寒冷使血浆去甲肾上腺素增加（P < 0.05），而咖啡因和运动均使肾上腺素增加（P < 0.05）。血清游离脂肪酸和甘油增加，但静息与运动之间或安慰剂与咖啡因之间没有差异。咖啡因对静息或运动时的呼吸交换率或耗氧量均无影响。运动试验并未显著使身体变暖，且在前30分钟导致血浆去甲肾上腺素浓度升高和平均皮肤温度降低。数据表明，皮肤温度刺激血浆去甲肾上腺素，而咖啡因影响很小。相反，咖啡因和运动刺激血浆肾上腺素，而寒冷影响最小。在本研究的范围内，在冷应激期间咖啡因没有产生热或代谢优势。
