Author(s): MATSUMURA, T., NONOYAMA, S., ENDO, K., FUKUZAWA, K., YAMAMOTO, T., YUUKI, I.W., DORA, K., KOJIMA, C., IEMITSU, M., ISAKA, T., HASHIMOTO, T., Institution: RITSUMEIKAN UNIVERSITY, Country: JAPAN, Abstract-ID: 2232

INTRODUCTION:
Much attention has been paid to the use of caffeine as a pre-workout supplement to improve athletic performance during acute bout of resistance exercise session (1). However, it is unclear whether pre-exercise caffeine ingestion subsequently affects exercise-induced muscle damage (EIMD) accompanied by reduced muscle functionality (e.g., force loss) for several days, because few studies have focused on post-exercise decreases in muscle force, as the reliable EIMD marker (2). Since higher eccentric exercise loads lead to greater EIMD (3), caffeine’s ergogenic effects may exacerbate EIMD by increasing eccentric loads during exercise. Here, this study examined the impact of pre-exercise caffeine ingestion on EIMD (i.e., reduced torque) after eccentric exercise, while focusing on the changes in eccentric loads induced by caffeine's ergogenic effects during exercise.
METHODS:
In double-blind, crossover trials, fifteen healthy young men ingested 6 mg/kg caffeine/placebo, followed by an eccentric exercise at 30–120° of knee angles: 100-times isokinetic eccentric maximal voluntary knee extensions in STUDY 1 (i.e., caffeine can change eccentric load) and 100-times isoload (fixed at 120% of concentric 1RM) eccentric leg extensions in STUDY 2 (i.e., caffeine cannot change eccentric load). In STUDY 1, torque-time integral (TTI) and angle-specific torque were calculated during the exercise as exercise performance. Maximal voluntary isometric torques (MVITs) of the knee extensors were evaluated at 24 and 48 h after the exercise as an indirect EIMD marker. The linear mixed-effects model and type III ANOVA were applied to detect the impact of caffeine on post-exercise MVITs. Repeated measures correlations were used to analyze relationships between eccentric load during exercise and EIMD in STUDY 1.
RESULTS:
In STUDY 1, caffeine significantly increased Total TTI (p=0.001) and torque during exercise than placebo, regardless of knee angle (p<0.001). However, caffeine produced lower post-exercise MVITs at 24 and 48 h than placebo (p<0.001). Conversely, there were no significant differences in post-exercise MVITs between conditions in STUDY 2 (p=0.242), emphasizing that the greatly reduced torque was derived from the caffeine-induced increase in eccentric load. In STUDY 1, post-exercise MVIT was negatively correlated with total TTI (r=-0.53, p=0.034) and torque at 90–120° knee angles (r=-0.54, p=0.034) but not at <90° knee angles (r=-0.34 to -0.06, p>0.05).
CONCLUSION:
Pre-exercise caffeine ingestion increases EIMD (greater torque reduction) for several days after eccentric exercise by increased eccentric load as caffeine’s ergogenic effect. Furthermore, increased eccentric loads at a long muscle length may particularly contribute to caffeine-induced greater EIMD. We should consider the potential impact for greater EIMD when using caffeine as a pre-workout supplement for resistance exercise.

1. Grgic. Sports Med. 2021
2. Matsumura et al. PharmaNutrition. 2026
3. Chen et al. J Appl Physiol. 2007