Effects of creatine on isometric bench-press performance in resistance-trained humans.
OBJECTIVE
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 x kg(-1) x dry weight muscle (median [range]). Four subjects in the Cr group were classified as "nonresponders" (< or =21 mmol x kg(-1) x dry weight muscle increase following Cr supplementation) and the remaining 17 subjects were classed as "responders" (> or =32 mmol x kg(-1) x 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.


CONCLUSIONS
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.
Kilduff
Liam P
LP
Centre for Exercise Science and Medicine, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, UK.
Vidakovic
Petar
P
Cooney
Gerard
G
Twycross-Lewis
Richard
R
Amuna
Paul
P
Parker
Matt
M
Paul
Lorna
L
Pitsiladis
Yannis P
YP
D000328:Adult; D001823:Body Composition / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects*; D003401:Creatine / Q000494:pharmacology*; D019587:Dietary Supplements; D004311:Double-Blind Method; D006801:Humans; D007537:Isometric Contraction / Q000187:drug effects*; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects*; D005082:Physical Exertion / Q000187:drug effects*; D013647:Task Performance and Analysis; D014891:Weight Lifting / Q000502:physiology*
D003401:Creatine