Ergogenic response to caffeine in resistance performance, perceived pain, and female sex hormones following muscular endurance in strength-trained eumenorrheic females during early follicular phase

This study investigates the ergogenic response to caffeine, in terms of repetitions to failure, time under tension, perceived pain, and female sex hormones (oestradiol and progesterone), following muscular endurance during the early follicular phase. Eleven strength-trained eumenorrheic females performed two consecutive trials (48 h apart). Using a double-blind crossover design, participants were randomly assigned to receive either caffeine (4 mg/kg) 1 h before exercise or a placebo. In each trial, participants performed as many repetitions of leg extension and hip adduction as possible at 65% of 1-RM. Two minutes of recovery were allocated between each exercise. Each repetition was performed at maximal velocity. Perceived pain was rated on an 11-point scale immediately after each exercise, and blood samples were drawn from each participant 30 min after completing the test. Data revealed a significant ergogenic response to caffeine in repetitions to failure for leg extension and hip adduction (p = .003 and p = .043, respectively); meanwhile, caffeine led to a significantly longer time under tension in leg extension (p = .001), with no differences in hip adduction (p = .053). In terms of perceived pain, no differences between trials were found for hip adduction (p = .724), but it was rated higher after leg extension in the caffeine trial, when compared to the placebo (p = .011). No differences were observed between trials regarding oestradiol and progesterone levels (p = .138 and p = .350, respectively). In conclusion, ingestion of 4 mg/kg of caffeine increased leg extension and hip adduction repetitions to failure, without main effects on perceived pain and sex hormones, in strength-trained eumenorrheic females during the early follicular phase.