Effects of caffeine on central and peripheral fatigue following closed-and open-loop cycling exercises

Abstract

We examined whether endurance performance and neuromuscular fatigue would be affected by caffeine ingestion during closed-and open-loop exercises. Nine cyclists performed a closed-loop (4,000-m cycling time trial) and an open-loop exercise (work rate fixed at mean power of the closed-loop trial) 60 min after ingesting caffeine (CAF, 5 mg/kg) or placebo (PLA, cellulose). Central and peripheral fatigue was quantified via pre-to post-exercise decrease in quadriceps voluntary activation and potentiated twitch force, respectively. Test sensitivity for detecting caffeine-induced improvements in exercise performance was calculated as the mean change in time divided by the error of measurement. Caffeine ingestion reduced the time of the closed-loop trial (PLA: 375.1±14.5 s vs CAF: 368.2±14.9 s, P=0.024) and increased exercise tolerance during the open-loop trial (PLA: 418.2±99.5 s vs CAF: 552.5±106.5 s, P=0.001), with similar calculated sensitivity indices (1.5, 90%CI: 0.7–2.9 vs 2.8, 90%CI: 1.9–5.1). The reduction in voluntary activation was more pronounced (P=0.019) in open-(–6.8±8.3%) than in closed-loop exercises (–1.9±4.4%), but there was no difference between open-and closed-loop exercises for the potentiated twitch force reduction (–25.6±12.8 vs –26.6±12.0%, P>0.05). Caffeine had no effect on central and peripheral fatigue development in either mode of exercise. In conclusion, caffeine improved endurance performance in both modes of exercise without influence on post-exercise central and peripheral fatigue, with the open-loop exercise imposing a greater challenge to central fatigue tolerance.