Pre-Exercise Caffeine Ingestion Leads to Greater Exercise-Induced Torque Reduction by Increasing Eccentric Load During Resistance Exercise.

PURPOSE: This study examined the impact of pre-exercise caffeine supplementation on post-exercise torque reduction, an indirect marker of exercise-induced muscle damage (EIMD), while focusing on the changes in eccentric load induced by the ergogenic effects of caffeine. METHODS: In double-blind, crossover trials, 15 healthy young men ingested 6 mg/kg caffeine or placebo, followed by an eccentric exercise task at 30-120° of knee extension: 100 isokinetic eccentric maximal voluntary knee extensions in Study 1 (i.e., variable eccentric load by caffeine) and 100 isoload (fixed at 120% of concentric one-repetition maximum) eccentric leg extensions in Study 2 (i.e., invariable eccentric load by caffeine). Maximal voluntary isometric torque (MVIT) of the knee extensors, an indirect EIMD marker, was evaluated at 24 and 48 h after exercise. RESULTS: In Study 1, caffeine supplementation resulted in higher eccentric torques during exercise (P ≤ 0.001), but lower post-exercise MVITs (P < 0.001) than placebo. Conversely, in Study 2, there were no significant differences in post-exercise MVITs between the conditions (P = 0.242). In Study 1, post-exercise MVITs were negatively correlated with the total torque-time integral (rrm = -0.53; P = 0.034). CONCLUSIONS: Pre-exercise caffeine supplementation induces greater exercise-induced torque reduction during the 48-h post-exercise period after eccentric exercise, potentially suggesting greater EIMD. Additionally, increased eccentric load in accordance with caffeine's ergogenic effect may contribute to this greater post-exercise torque-reduction. Therefore, the potential impact on post-exercise muscle function should be considered when caffeine is used as a preworkout supplement for resistance exercise.