Foad Abigail J, Beedie Christopher J, Coleman Damian A
Canterbury Christ Church University, Canterbury, United Kingdom.
Med Sci Sports Exerc. 2008 Jan;40(1):158-65. doi: 10.1249/mss.0b013e3181593e02.
The ergogenic effects of caffeine are well documented. Research has yet to examine any psychological contribution to this effect.
To explore the psychological and pharmacological effects of caffeine in laboratory cycling performance.
Fourteen male competitive cyclists performed 14 40-km time trials (eight experimental interspersed with six baseline). The experimental phase consisted of two trials for each of four experimental conditions: informed caffeine/received caffeine, informed no treatment/received caffeine, informed caffeine/received placebo, and informed no treatment/received no treatment. Conditions were nonrandomized. ANOVA was used to estimate main effects and interactions for mean values of power, heart rate, blood lactate, and maximal oxygen uptake. Probabilistic inferences for mean power were based on a smallest worthwhile change of 1.5%.
Relative to baseline, a very likely beneficial main effect of receiving caffeine (3.5%; 95% confidence interval 1.5 to 5.5%), and a possibly beneficial main effect of being informed of caffeine (0.7%; -0.7 to 2.1%) were observed. A substantial interaction between belief and pharmacology indicated that caffeine exerted a greater effect on performance in conditions when subjects were informed that they had not ingested it, whereas belief exerted a greater influence on performance in the absence of caffeine (2.6%; -0.7 to 5.9%). A possibly harmful negative placebo (nocebo) effect was observed when subjects were correctly informed that they had ingested no caffeine (-1.9%; -4.1 to 0.3%). No clinically significant changes relative to baseline were observed in mean heart rate. Clear and substantial increases in blood lactate were evident after receipt of caffeine. Data for mean oxygen uptake were unclear.
Our data support the ergogenic efficacy of caffeine but suggest that both positive and negative expectations impact performance.
咖啡因的促力效应已有充分记录。但研究尚未考察这种效应的任何心理因素。
探讨咖啡因对实验室自行车运动表现的心理和药理作用。
14名男性竞技自行车运动员进行了14次40公里计时赛（8次实验性计时赛穿插6次基线计时赛）。实验阶段包括针对四种实验条件各进行两次试验：告知摄入咖啡因/实际摄入咖啡因、告知未治疗/实际摄入咖啡因、告知摄入咖啡因/实际摄入安慰剂、告知未治疗/未接受任何处理。条件未随机分配。采用方差分析来估计功率、心率、血乳酸和最大摄氧量平均值的主效应和交互作用。平均功率的概率推断基于最小有价值变化1.5%。
相对于基线，观察到摄入咖啡因有非常可能的有益主效应（3.5%；95%置信区间1.5%至5.5%），以及被告知摄入咖啡因有可能的有益主效应（0.7%；-0.7%至2.1%）。信念与药理学之间存在显著交互作用，表明当受试者被告知未摄入咖啡因时，咖啡因对表现的影响更大，而在未摄入咖啡因的情况下，信念对表现的影响更大（2.6%；-0.7%至5.9%）。当受试者被告知正确摄入了无咖啡因物质时，观察到可能有害的负安慰剂（反安慰剂）效应（-1.9%；-4.1%至0.3%）。相对于基线，平均心率未观察到临床显著变化。摄入咖啡因后血乳酸明显大幅增加。平均摄氧量的数据不明确。
我们的数据支持咖啡因的促力功效，但表明积极和消极期望都会影响表现。
