The present study aimed to evaluate the effects of long-term resistance training and caffeine supplementation on strength and muscular adaptations. Twenty-eight participants were randomly assigned to either the caffeine (CAF) or placebo (PLA) group, of whom 26 completed the intervention. Supplementation was administered one hour prior to thrice-weekly upper-body resistance training sessions over the six-week period. The subsequent assessments were carried out prior to and following the intervention: one-repetition maximum (bench press and bench pull 1RM), muscle endurance (bench press to failure at 60% of 1RM), muscle thickness of the biceps and triceps brachii, and body composition. An interaction between time and group was observed for both biceps (p = 0.009) and triceps (p = 0.049) muscle thickness. Effect size analyses showed a greater increase in biceps muscle thickness in the CAF group than in the PLA group. A similar analysis of triceps muscle thickness indicated a greater increase in the CAF group. No other significant between-group differences were observed. These results suggest that prolonged caffeine supplementation may enhance muscle growth in recreationally active men,while strength and body composition changes remained comparable between groups, indicating a potentially limited effect of caffeine on these outcomes.

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