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Randomized Controlled Trial
. 2019 Jan 23;14(1):e0210275.
doi: 10.1371/journal.pone.0210275. eCollection 2019.

Time course of tolerance to the performance benefits of caffeine

Beatriz Lara  1 , Carlos Ruiz-Moreno  1 , Juan José Salinero  1 , Juan Del Coso  1
Affiliations
Randomized Controlled Trial

Time course of tolerance to the performance benefits of caffeine

Beatriz Lara et al. PLoS One. .

Abstract

The ergogenic effect of acute caffeine ingestion has been widely investigated; however, scientific information regarding tolerance to the performance benefits of caffeine, when ingested on a day-to-day basis, is scarce. The aim of this investigation was to determine the time course of tolerance to the ergogenic effects of a moderate dose of caffeine. Eleven healthy active participants took part in a cross-over, double-blind, placebo-controlled experiment. In one treatment, they ingested 3 mg/kg/day of caffeine for 20 consecutive days while in another they ingested a placebo for 20 days. Each substance was administered daily in an opaque unidentifiable capsule, and the experimental trials started 45 min after capsule ingestion. Two days before, and three times per week during each 20-day treatment, aerobic peak power was measured with an incremental test to volitional fatigue (25 W/min) and aerobic peak power was measured with an adapted version of the Wingate test (15 s). In comparison to the placebo, the ingestion of caffeine increased peak cycling power in the incremental exercise test by ~4.0 ±1.3% for the first 15 days (P<0.05) but then this ergogenic effect lessened. Caffeine also increased peak cycling power during the Wingate test on days 1, 4, 15, and 18 of ingestion by ~4.9 ±0.9% (P<0.05). In both tests, the magnitude of the ergogenic effect of caffeine vs. placebo was higher on the first day of ingestion and then progressively decreased. These results show a continued ergogenic effect with the daily ingestion of caffeine for 15-18 days; however, the changes in the magnitude of this effect suggest progressive tolerance.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Experimental design of the investigation.
Caffeine (3 mg/kg/day) or a placebo was administered for 20 consecutive days in a randomized order. Exercise performance was measured on day 0 (48 h before treatment) and on days 1, 4, 6, 8, 11, 13, 15, 18 and 20 with each protocol. Exercise performance assessment included a graded exercise test on a cycle ergometer to volitional fatigue and the 15-s Wingate test 45 min after the ingestion of the assigned capsule. Only on day 11 during each treatment, participants ingested the capsule after the end of the exercise.
Fig 2
Fig 2. Peak cycling power (Wmax) obtained during a graded exercise test with the administration of 3 mg/kg/day of caffeine or a placebo for 20 consecutive days.
The upper panel depicts the effect size (± 90% confidence intervals) for all pairwise comparisons. Only effect sizes with a possible likelihood of difference (>25%) are categorized: (++++) most likely, (+++) very likely, (++) likely, (+) possibly. The lower panel depicts data presented as mean ± standard deviation. The data have been normalized with respect to the values obtained on day 0 of each treatment to provide a better comparison of the caffeine ergogenic effect in the studied variables. (*) Caffeine different from placebo for the same day, P < 0.05. (†) Different from day 0 within the same treatment, P < 0.05.
Fig 3
Fig 3. Maximal oxygen uptake (VO2max) obtained during a graded exercise test with the administration of 3 mg/kg/day of caffeine or a placebo for 20 consecutive days.
The upper panel depicts the effect size (± 90% confidence intervals) for all pairwise comparisons. Only effect sizes with a possible likelihood of difference (>25%) are categorized: (++++) most likely, (+++) very likely, (++) likely, (+) possibly. The lower panel depicts data presented as mean ± standard deviation. The data have been normalized with respect to the values obtained on day 0 of each treatment to provide a better comparison of the caffeine ergogenic effect in the studied variables. (*) Caffeine different from placebo for the same day, P < 0.05. (†) Different from day 0 within the same treatment, P < 0.05.
Fig 4
Fig 4. Peak cycling power obtained during an adapted version of the Wingate test (all-out 15 s sprint) with the administration of 3 mg/kg/day of caffeine or a placebo for 20 consecutive days.
The upper panel depicts the effect size (± 90% confidence intervals) for all pairwise comparisons. Only effect sizes with a possible likelihood of difference (>25%) are categorized: (++++) most likely, (+++) very likely, (++) likely, (+) possibly. The lower panel depicts data presented as mean ± standard deviation. The data have been normalized with respect to the values obtained on day 0 of each treatment to provide a better comparison of the caffeine ergogenic effect in the studied variables. (*) Caffeine different from placebo for the same day, P < 0.05. (†) Different from day 0 within the same treatment, P < 0.05.
Fig 5
Fig 5. Mean cycling power obtained during an adapted version of the Wingate test (all-out 15 s sprint) with the administration of 3 mg/kg/day of caffeine or a placebo for 20 consecutive days.
The upper panel depicts the effect size (± 90% confidence intervals) for all pairwise comparisons. Only effect sizes with a possible likelihood of difference (>25%) are categorized: (++++) most likely, (+++) very likely, (++) likely, (+) possibly. The lower panel depicts data presented as mean ± standard deviation. The data have been normalized with respect to the values obtained on day 0 of each treatment to provide a better comparison of the caffeine ergogenic effect in the studied variables. (*) Caffeine different from placebo for the same day, P < 0.05. (†) Different from day 0 within the same treatment, P < 0.05.
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