The Effect of Acute Caffeine Intake on Resistance Training Volume, Prooxidant- Antioxidant Balance and Muscle Damage Markers Following a Session of Full- Body Resistance Exercise in Resistance-Trained Men Habituated to Caffeine

No previous study has analyzed the impact of caffeine intake on prooxidant-antioxidant balance and muscle damage following re-sistance exercise. The aim of this study was to determine the ef-fect of 3 mg/kg of caffeine on the number of repetitions and the prooxidant-antioxidant balance and muscle damage after a ses-sion of full-body resistance exercise. Ten resistance-trained men habituated to caffeine participated in a randomized, crossover and double-blind experiment. Each participant performed two identi-cal resistance training sessions after the intake of 3 mg/kg of caf-feine or a placebo. Blood was collected before and 60 min after substance intake, just after exercise, 60 minutes after exercise, and 24 hours after testing to evaluate the activity of antioxidant enzymes (superoxide dismutase, glutathione peroxidase, cata-lase), non-enzymatic antioxidants (reduced glutathione, uric acid) levels of oxidative stress markers (plasma malondialdehyde) and muscle damage markers (creatine kinase, lactate dehydrogenase). There were no significant differences between placebo and caf-feine conditions in the total number of repetitions (180 & PLUSMN; 15 vs 185 & PLUSMN; 14 repetitions, respectively; p = 0.276; Effect size [ES] = 0.34), the total time under tension (757 & PLUSMN; 71 vs 766 & PLUSMN; 56 s, re-spectively; p = 0.709; ES = 0.14) or the rating of perceived exer-tion (13.8 & PLUSMN; 2.7 vs 14.7 & PLUSMN; 2.7 a.u., respectively; p = 0.212; ES = 0.32). Reduced glutathione concentration obtained 1 hour after exercise was higher with caffeine than with placebo (p = 0.047), without significant difference between conditions for any other prooxidant-oxidant or muscle damage marker at any time point (p > 0.050 for all). The oral intake of 3 mg/kg of caffeine by re-sistance-trained men habituated to caffeine did not enhance the number of repetitions during a medium load full-body resistance training session to failure and had a minimal impact on the proox-idant-antioxidant balance and muscle damage. The study was reg-istered prospectively at ClinicalTrials.gov with the following ID: NCT05230303.