Van Soeren M H, Graham T E
School of Nursing, Faculty of Health Sciences, University of Western Ontario, London, Ontario N6A 5C1.
J Appl Physiol (1985). 1998 Oct;85(4):1493-501. doi: 10.1152/jappl.1998.85.4.1493.
In this study the effects of acute caffeine ingestion on exercise performance, hormonal (epinephrine, norepinephrine, insulin), and metabolic (free fatty acids, glycerol, glucose, lactate, expired gases) parameters during short-term withdrawal from dietary caffeine were investigated. Recreational athletes who were habitual caffeine users (n = 6) (maximum oxygen uptake 54.5 +/- 3.3 ml x kg-1 x min-1 and daily caffeine intake 761.3 +/- 11.8 mg/day) were tested under conditions of no withdrawal and 2-day and 4-day withdrawal from dietary caffeine. There were seven trials in total with a minimum of 10 days between trials. On the day of the exercise trial, subjects ingested either dextrose placebo or 6 mg/kg caffeine in capsule form 1 h before cycle ergometry to exhaustion at 80-85% of maximum oxygen uptake. Test substances were assigned in a random, double-blind manner. A final placebo control trial completed the experiment. There was no significant difference in any measured parameters among days of withdrawal after ingestion of placebo. At exhaustion in the 2- and 4-day withdrawal trials, there were significant increases in plasma norepinephrine in response to caffeine ingestion. Caffeine-induced increases in serum free fatty acids occurred after 4 days and only at rest. Subjects responded to caffeine with increases in plasma epinephrine (P < 0.05) at exhaustion and prolonged exercise time in all caffeine trials compared with placebo, regardless of withdrawal from caffeine. It is concluded that increased endurance is unrelated to hormonal or metabolic changes and that it is not related to prior caffeine habituation in recreational athletes.
在本研究中，调查了急性摄入咖啡因对短期停止摄入膳食咖啡因期间运动表现、激素（肾上腺素、去甲肾上腺素、胰岛素）和代谢（游离脂肪酸、甘油、葡萄糖、乳酸、呼出气体）参数的影响。对习惯性摄入咖啡因的休闲运动员（n = 6）（最大摄氧量54.5±3.3 ml·kg⁻¹·min⁻¹，每日咖啡因摄入量761.3±11.8 mg/天）在不停止摄入咖啡因、停止摄入膳食咖啡因2天和4天的条件下进行了测试。总共进行了七次试验，试验之间至少间隔10天。在运动试验当天，受试者在进行自行车测力计运动至力竭（达到最大摄氧量的80 - 85%）前1小时，以胶囊形式摄入葡萄糖安慰剂或6 mg/kg咖啡因。测试物质以随机、双盲的方式分配。最后进行了一次安慰剂对照试验以完成该实验。摄入安慰剂后，在停止摄入咖啡因的各天之间，任何测量参数均无显著差异。在2天和4天停止摄入咖啡因的试验中，力竭时，血浆去甲肾上腺素因摄入咖啡因而显著增加。咖啡因诱导的血清游离脂肪酸增加在4天后出现，且仅在静息时出现。与安慰剂相比，在所有咖啡因试验中，受试者在力竭时血浆肾上腺素增加（P < 0.05），并且运动时间延长，无论是否停止摄入咖啡因。得出的结论是，耐力增加与激素或代谢变化无关，并且与休闲运动员先前的咖啡因习惯无关。
