Effects of acute creatine monohydrate supplementation on leucine kinetics and mixed-muscle protein synthesis

Creatine monohydrate (CrM) supplementation during resistance exercise train ing results in a greater increase in strength and fat-free mass than placeb o. Whether this is solely due to an increase in intracellular water or whet her there may be alterations in protein turnover is not clear at this point . We examined the effects of CrM supplementation on indexes of protein meta bolism in young healthy men (n = 13) and women (n = 14). Subjects were rand omly allocated to CrM (20 g/day for 5 days followed by 5 g/day for 3-4 days ) or placebo (glucose polymers) and tested before and after the supplementa tion period under rigorous dietary and exercise controls. Muscle phosphocre atine, creatine, and total creatine were measured before and after suppleme ntation. A primed-continuous intravenous infusion of L-[1-C-13] leucine and mass spectrometry were used to measure mixed-muscle protein fractional syn thetic rate and indexes of whole body leucine metabolism (nonoxidative leuc ine disposal), leucine oxidation, and plasma leucine rate of appearance. Cr M supplementation increased muscle total creatine (+13.1%, P < 0.05) with a trend toward an increase in phosphocreatine (+8.8%, P = 0.09). CrM supplem entation did not increase muscle fractional synthetic rate but reduced leuc ine oxidation (-19.6%) and plasma leucine rate of appearance (-7.5%, P < 0. 05) in men, but not in women. CrM did not increase total body mass or fat-f ree mass. We conclude that shortterm CrM supplementation may have anticatab olic actions in some proteins (in men), but CrM does not increase whole bod y or mixed-muscle protein synthesis.