In the present study, submaximal oxygen consumption was 8-9%
lower following creatine supplementation than following placebo near the end of two hours of cycling (P < 0.05), although the cause of this reduced oxygen consumption is unknown. No previous studies of creatine supplementation and endurance exercise have SB431542 in vivo contained reports of respiratory exchange ratio. We found no effect of supplementation on respiratory exchange ratio, suggesting that creatine supplementation does not alter fuel selection. There was also no difference between creatine and placebo groups in the change in muscle glycogen during the cycling bout. There was a higher muscle glycogen concentration five minutes prior to the end of exercise in the post-creatine cycling bout compared to the post-placebo cycling bout, but this was likely due to the slightly elevated muscle glycogen content prior to the post-supplementation exercise in the creatine group. The vast majority of previous studies of creatine supplementation BKM120 order have used a five to ten day supplementation at 20 g/day. Hultman et al. [16] demonstrated that the high loading phase of creatine is not necessary if a longer supplementation
period (28 days) is used. Their protocol of three g/day for one month had not been replicated prior to the current study. We have found that 28 days of creatine supplementation at three g/day increases muscle creatine phosphate
to levels above a placebo group post supplementation. The increases in muscle creatine phosphate and total creatine VAV2 were of similar magnitude (approx. 10 and 20 mmol/kg, respectively) to those demonstrated by Hultman et al. [16]. However, there also appeared to be increases, though not significant, in our placebo group of 5 mmol/kg and 10 mmol/kg and for creatine phosphate and total creatine, respectively. These data, in combination with our performance data demonstrating an increased performance that was not dependent upon the type of supplementation (creatine or placebo), highlight the importance of using a placebo group and a double-blind protocol. Although Hultman et al. included a placebo group in their study design, they did not take muscle biopsies from the control group. Conclusions The present data support the findings of Hultman et al. [16] with respect to increases in muscle creatine phosphate with creatine supplementation at 3 g/day for 28 days. The creatine supplementation was also associated with higher pre-exercise body weight as well as higher muscle glycogen concentration and plasma volume near the end of two hours of cycling after creatine supplementation compared to placebo. It can be concluded that 28 days of creatine supplementation increased resting muscle creatine phosphate, muscle glycogen content and plasma volume during exercise.