Effects of creatine on isometric bench-press performance in resistance-trained humans

Purpose: The purpose of this study was to investigate the effects of creatine (Cr) supplementation on force generation during an isometric bench-press in resistance-trained men. Methods: 32 resistance-trained men were matched for peak isometric force and assigned in double-blind fashion to either a Cr or placebo group. Subjects performed an isometric bench-press test involving five maximal isometric contractions before and after 5 d of Cr (20 g.d(-1) Cr + 180 g.d(-1) dextrose) or placebo (200 g.d(-1) dextrose). Body composition was measured before and after supplementation. Subjects completed 24-h urine collections throughout the study period: these were subsequently analyzed to provide total Cr and creatinine excretion. Results: The amount of Cr retained over the supplementation period was 45 +/- 18 g (mean +/- SD), with an estimated intramuscular Cr storage of 43 (13-61) mmol.kg(-1).dry weight muscle (median [range]). Four subjects in the Cr group were classified as "nonresponders" (less than or equal to21 mmol.kg(-1).dry weight muscle increase following Cr supplementation) and the remaining 17 subjects were classed as "'responders" (greater than or equal to32 mmol.kg(-1).dry weight muscle). For the Cr group, peak force and total force pre- or post-supplementation were not different from placebo, However. when the analysis was confined to the responders. both the change in peak, force [Repetition 2: 59(81) N vs -26(85) N Repetition 3: 45(59) N vs -26(64) N) and the change in total force (Repetition 1: 1471(1274) N vs 209(1517) N Repetition 2: 1575(1254) N vs 196(1413) N: Repetition 3: 1278(1245) N vs -3(1118) N: Repetition 4: 918(935) N vs -83(1095) N] post-supplementation were significantly greater compared with the placebo group (P < 0.01). For the Cr group, estimated Cr uptake was inversely correlated with training status (r = -0.68, N = 21, P = 0.001). Cr significantly increased body weight (84.1 = 8.6 kg pre- vs 85.3 +/- 8.3 kg post-supplementation) and fat-free mass (71.8 +/- 6.0 kg pre- vs 72.6 +/- 6.0 kg post-supplementation), with the magnitude of increase being significantly greater in :he responder group than in the placebo group. Conclusion: Five days of Cr supplementation increased body weight and fat-free body mass in resistance-trained men who were classified as responders. Peak force and total force during a repeated maximal isometric bench-press test were also significantly greater in the responders compared to the placebo group,