Effects of caffeine on repeated sprint ability, reactive agility time, sleep and next day performance

Aim. This study assessed the effects of caffeine on repeated sprint ability (RSA), reactive agility time (RAT), sleep and next day exercise performance. Methods. Ten moderately trained male athletes (single-blind, randomized, crossover design) ingested either caffeine (6 mg.kg(-1) bm) or placebo 1 h before exercise. Trials were performed on the same day one week apart. Performance measures included a RAT test (10 trialsx10.2 m, separated by 30 s), followed by 7 min of active recovery and then a RSA test (five sets of 6x20 in sprints with 25 or 60 s of recovery). The RSA was then followed by 5 min of active recovery and another RAT. That night, participants wore a wrist sleep actigraph to bed. Next day, participants repeated the RAT and the first set of the RSA tests. Results. Significant improvements were demonstrated after caffeine ingestion compared to placebo for the combined total time of each set (TT; combined sets 1, 3, 5; 58.947 +/- 1.88 vs. 59.683 +/- 2.54 s, respectively; P=0.05), best sprint time (BT; next day performance; 3.176 +/- 0.10 vs. 3.230 +/- 0.12 s, respectively, P=0.01), and % decrement (combined sets 2,4; 2.866 +/- 1.24 vs. 3.801 +/- 1.69 s, respectively; P=0.02). Moderate to strong effect sizes were found for % decrement for set 2 (Cohen's d=-0.82; 1.312 +/- 0.65 vs. 2.110 +/- 1.20 s for caffeine and placebo conditions, respectively) and for sets 2 and 4 combined (Cohen's d=-0.63; 2.866 +/- 1.24 vs. 3.801 +/- 1.69 for caffeine and placebo conditions, respectively). No significant differences were found for RAT or for sleep measures (P > 0.05). Conclusion. Caffeine improved RSA, including next day performance, but had little effect on RAT or sleep parameters.