Sex differences on the acute effects of caffeine on maximal strength and muscular endurance

The aim of this study was to look at the effects of caffeine on strength performance and to examine any differences between sexes. Sixteen moderately active, resistance-trained individuals (10 males and 8 females) performed 2 trials (excluding a familiarisation trial). The effect of 5 mg/kg body mass (BM) caffeine or a placebo on bench press (BP) one repetition maximum (1RM), squat 1RM, the number of BP reps to failure at 40% 1RM (total weight lifted; TWL), pain rating (0-10) were recorded after each final successful lift. BP 1RM was significantly greater (P=0.016), with an increase of 5.91% for males and an increase of 10.69% for females. However, there was no sex difference in squat 1RM with males producing 130.3 +/- 27.8 and 134.0 +/- 28.9 kg and females producing 66.9 +/- 6.2 and 65.3 +/- 7.0 kg for placebo and caffeine, respectively. TWL tended to increase with caffeine for males from 1,246.8 +/- 704.9 to 1,545.5 +/- 920.3 kg; with females having no effect of caffeine (397.8 +/- 245.1 to 398.8 +/- 182.7kg; P=0.06). Caffeine had no effect on pain perception. This study found that 5 mg/kg BM caffeine improved BP 1RM in resistance-trained males and females. However, for TWL there was a tendency towards improvement in males only, suggesting a sex difference to caffeine ingestion for TWL.