Ahrens Jennifer N, Crixell Sylvia H, Lloyd Lisa K, Walker John L
Department of Health, Physical Education, and Recreation, Texas State University-San Marcos, 78666, USA.
J Strength Cond Res. 2007 Feb;21(1):164-8. doi: 10.1519/00124278-200702000-00029.
Although the effects of caffeine ingestion on athletic performance in men have been studied extensively, there is limited previous research examining caffeine's effects on women of average fitness levels participating in common modes of physical activity. The purpose of this study was to determine the effect of 2 levels of caffeine dosage on the metabolic and cardiorespiratory responses to treadmill walking in women. Subjects were 20 women (19-28 years of age) of average fitness, not habituated to caffeine. Each subject was assigned randomly a 3-mg x kg(-1) dose of caffeine, 6-mg x kg(-1) dose of caffeine, and placebo for 3 trials of moderate steady-state treadmill walking at 94 m x min(-1) (3.5 mph). Steady-state rating of perceived exertion (RPE), heart rate (HR), respiratory exchange ratio (RER), weight-relative VO2, %VO2max reserve (%VO2R), and rate of energy expenditure (REE) were measured during each trial. Repeated measures analysis of variance revealed that a 6-mg x kg(-1), but not a 3-mg x kg(-1) dose of caffeine increased VO2 (p = 0.04), REE (p = 0.03), and %VO2R (p = 0.03), when compared to the placebo. Caffeine had no effect on RPE, HR, or RER. No significant differences were observed between the placebo trials and the 3-mg x kg(-1) dose trials. Although a 6-mg x kg(-1) dose of caffeine significantly increased REE during exercise, the observed increase (approximately 0.23 kcal x min(-1)) would not noticeably affect weight loss. Because caffeine had no effect on RPE, it would not be prudent for a trainer to recommend caffeine in order to increase a woman's energy expenditure or to decrease perception of effort during mild exercise. These data also demonstrate that caffeine intake should not interfere with monitoring walking intensity by tracking exercise heart rate in women.
尽管摄入咖啡因对男性运动表现的影响已得到广泛研究，但此前关于咖啡因对参与常见体育活动的普通健康水平女性的影响的研究有限。本研究的目的是确定两种咖啡因剂量水平对女性在跑步机上行走时的代谢和心肺反应的影响。研究对象为20名平均健康水平、不常摄入咖啡因的女性（年龄在19至28岁之间）。每位受试者被随机分配接受3毫克/千克体重的咖啡因剂量、6毫克/千克体重的咖啡因剂量以及安慰剂，进行3次在跑步机上以94米/分钟（3.5英里/小时）的速度进行的中等强度稳态行走试验。在每次试验期间测量稳态主观用力程度（RPE）、心率（HR）、呼吸交换率（RER）、相对体重的摄氧量、最大摄氧量储备百分比（%VO2R）以及能量消耗率（REE）。重复测量方差分析显示，与安慰剂相比，6毫克/千克体重而非3毫克/千克体重的咖啡因剂量可增加摄氧量（p = 0.04）、能量消耗率（p = 0.03）以及最大摄氧量储备百分比（p = 0.03）。咖啡因对主观用力程度、心率或呼吸交换率没有影响。在安慰剂试验和3毫克/千克体重剂量试验之间未观察到显著差异。尽管6毫克/千克体重的咖啡因剂量在运动期间显著增加了能量消耗率，但观察到的增加量（约0.23千卡/分钟）不会对体重减轻产生明显影响。由于咖啡因对主观用力程度没有影响，因此教练为增加女性的能量消耗或减轻轻度运动时的用力感知而推荐咖啡因是不明智的。这些数据还表明，摄入咖啡因不应干扰通过监测女性运动心率来监测行走强度。
