Caffeine Increases Endurance Performance via Changes in Neural and Muscular Determinants of Performance Fatigability

Purpose In the present study, we tested the hypothesis that caffeine would increase endurance performance via attenuation of neural and muscular determinants of performance fatigability during high-intensity, whole-body exercise. Methods Ten healthy males cycled until exhaustion (89% +/- 2% of V?O-2max) after the ingestion of caffeine or placebo. During another four visits, the same exercise was performed after either caffeine or placebo ingestion but with exercise discontinued after completing either 50% or 75% of the duration of placebo trial. An additional trial with caffeine ingestion was also performed with interruption at the placebo time to exhaustion (isotime). Performance fatigability was measured via changes in maximal voluntary contraction, whereas neural and muscular determinants of performance fatigability were quantified via preexercise to postexercise decrease in quadriceps voluntary activation (VA) and potentiated twitch force, respectively. Results Compared with the placebo, caffeine increased time to exhaustion (+14.4 +/- 1.6%, P = 0.017, 314.4 +/- 47.9 vs 354.9 +/- 40.8 s). Caffeine did not change the rate of decline in maximal voluntary contraction (P = 0.209), but caffeine reduced the twitch force decline at isotime when stimulating at single twitch (-58.6 +/- 22.4 vs -45.7 +/- 21.9%, P = 0.014) and paired 10 Hz electrical stimuli (-37.3 +/- 13.2 vs -28.2 +/- 12.9%, P = 0.025), and reduced the amplitude of electromyography signal during cycling at isotime (P = 0.034). The decline in VA throughout the trial was lower (P = 0.004) with caffeine (-0.5 +/- 4.2%) than with placebo (-5.8 +/- 8.5%). Caffeine also maintained peripheral oxygen saturation at higher levels (95.0 +/- 1.9%) than placebo (92.0 +/- 6.2%, P = 0.016). Conclusions Caffeine ingestion improves performance during high-intensity, whole-body exercise via attenuation of exercise-induced reduction in VA and contractile function.