Effect of creatine supplementation on metabolism and performance in humansduring intermittent sprint cycling

This double blind study investigated the effect of oral creatine supplement ation (CrS) on 4 x 20 s of maximal sprinting on an air-braked cycle ergomet er. Each sprint was separated by 20 s of recovery. A group of 16 triathlete s [mean age 26.6 (SD 5.1) years. mean body mass 77.0 (SD 5.8) kg, mean body fat 12.9 (SD 4.6)%, maximal oxygen uptake 4.86 (SD 0.7) 1 min(-1)] perform ed an initial 4 x 20 s trial after a muscle biopsy sample had been taken at rest. The subjects were then matched on their total intramuscular creatine content (TCr) before being randomly assigned to groups to take by mouth ei ther a creatine supplement (CRE) or a placebo (CON) before a second 4 x 20 s trial. PL muscle biopsy sample was also taken immediately before this sec ond trial. The CrS of 100 g comprised 4 x 5 g for 5 days. The initial mean TCr were 112.5 (SD 8.7) and 112.5 (SD 10.7) mmol (.) kg(-1) dry mass for CR E and CON, respectively. After creatine loading and placebo ingestion respe ctively, CRE [128.7 (SD 11.8)mmol (.) kg(-1) dry mass] had a greater (P = 0 .01) TCr than CON [112.0 (SD 10.0) mmol kg(-1) dry mass]. While the increas e in free creatine for CRE was statistically significant (P = 0.034), this was not so for the changes in phosphocreatine content [trial 1: 75.7 (SD 6. 9), trial 2.84.7 (SD 11.0) mmol (.) kg(-1) dry mass, P = 0.091]. There were no significant differences between CRE and CON for citrate synthase activi ty (P = 0.163). There was a tendency towards improved performance in terms of I s peak power tin watts P = 0.07; in watts per kilogram P = 0.05), 5 s peak power tin watts P = 0.08) and fatigue index (P = 0.08) after CrS for s print 1 of the second trial. However, there was no improvement for mean pow er tin watts P = 0.15; in watts per kilogram P = 0.1) in sprint 1 or for an y performance values in subsequent sprints. Our results suggest that, while CrS elevates the intramuscular stores of free creatine, this does not have an ergogenic effect on 4 x 20 s all-out cycle sprints with intervening 20- s rest periods.