KILDUFF, L. P., P. VIDAKOVIC, G. COONEY, R. TWYCROSS-LEWIS, P. AMUNA, M. PARKER, L. PAUL, and Y. P. PITSILADIS. Effects of creatine on isometric bench-press performance in resistance-trained humans. Med. Sci. Sports Exerc., Vol. 34, No. 7, pp. 1176–1183, 2002.
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” (≤21 mmol·kg−1·dry weight muscle increase following Cr supplementation) and the remaining 17 subjects were classed as “responders” (≥32 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 the 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.