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摘要
This study examined effects of 4weeks of caffeine supplementation on endurance performance. Eighteen low-habitual caffeine consumers (<75mgday(-1)) were randomly assigned to ingest caffeine (1.5-3.0mgkg(-1)day(-1); titrated) or placebo for 28days. Groups were matched for age, body mass, V.O-2peak and W-max (P>0.05). Before supplementation, all participants completed one V.O-2peak test, one practice trial and 2 experimental trials (acute 3mgkg(-1) caffeine [precaf] and placebo [testpla]). During the supplementation period a second V.O-2peak test was completed on day 21 before a final, acute 3mgkg(-1) caffeine trial (postcaf) on day 29. Trials consisted of 60min cycle exercise at 60% V.O-2peak followed by a 30min performance task. All participants produced more external work during the precaf trial than testpla, with increases in the caffeine (383.3 +/- 75kJ vs. 344.9 +/- 80.3kJ; Cohen's d effect size [ES]=0.49; P=0.001) and placebo (354.5 +/- 55.2kJ vs. 333.1 +/- 56.4kJ; ES=0.38; P=0.004) supplementation group, respectively. This performance benefit was no longer apparent after 4weeks of caffeine supplementation (precaf: 383.3 +/- 75.0kJ vs. postcaf: 358.0 +/- 89.8kJ; ES=0.31; P=0.025), but was retained in the placebo group (precaf: 354.5 +/- 55.2kJ vs. postcaf: 351.8 +/- 49.4kJ; ES=0.05; P>0.05). Circulating caffeine, hormonal concentrations and substrate oxidation did not differ between groups (all P>0.05). Chronic ingestion of a low dose of caffeine develops tolerance in low-caffeine consumers. Therefore, individuals with low-habitual intakes should refrain from chronic caffeine supplementation to maximise performance benefits from acute caffeine ingestion.
- 出版日期2017
