GENDER DIFFERENCES IN RESPONSE TO TWICE-A-WEEK CREATINE SUPPLEMENTATION DURING RESISTANCE TRAINING

PURPOSE: To examine the effects of twice-a-week creatine supplementation during resistance training on muscle mass and strength of males and females. METHODS: Eleven males (age:26.4 y; weight:83 kg) and 10 females (age:27.9y; weight:68.1 kg) with moderate resistance training experience (5.6y) were randomized (double blind) to receive either creatine (0.2g per kg body mass) or placebo (maltodextrine) twice per week. All subjects engaged in periodized resistance training (12 exercises, 3–4 sets of 4–10 repetitions) four times per week over 6 weeks. Muscle mass was measured by dual energy x-ray absorptiometry and strength was measured by bench press and leg press 1-repetition maximum before and after training. RESULTS: There was a group x gender interaction for relative change in muscle mass (p = 0.02). Males supplemented with creatine had greater increases in muscle mass (8.3%) than males on placebo (3.9%), females on creatine (2.9%) and females on placebo (2.4%) (all p < 0.01). There were no differences between the other groups. There was a trend for a group effect for relative change in bench press strength (p = 0.052), with subjects on creatine increasing by 33% and those on placebo increasing by 21%. Interestingly, there was a gender effect for relative change in bench press strength, with females demonstrating a greater increase (35%) than males (19%). There were no differences between groups for relative increase in leg press strength. CONCLUSION: Creatine supplementation enhanced the increase in muscle mass during resistance training for males, but not for females. Creatine supplementation tended to enhance the increase in bench press strength, regardless of gender. Creatine supplementation had no effect on leg press strength. Supported by Muscle Tech. Research and Development Inc.