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.
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.
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.
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.
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.
1Centre for Exercise Science and Medicine, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, UK;
2Sport and Exercise Science Research Centre, South Bank University, London, UK;
3School of Chemical and Life Sciences, University of Greenwich, London, UK; and
4Department of Physiotherapy, Podiatry and Radiography, Glasgow Caledonian University, Glasgow, Scotland, UNITED KINGDOM
Submitted for publication August 2001.
Accepted for publication February 2002.