The effects of creatine monohydrate supplementation on creatine transporter activity and creatine metabolism in resistance trained males.
Creatine is a nutritional supplement that is used for its potential performance enhancing (ergogenic) benefits. It constitutes an important component of the immediate energy system, by which ATP is regenerated during intense physical activity. Oral creatine supplementation has been shown to provide numerous benefits, including increases in lean muscle mass, muscular strength, and enhanced performance in various athletic capacities. The creatine transporter is a transmembrane protein that mediates the entry of creatine from the circulation into the muscle cell. Little is understood about the importance of the creatine transporter in controlling the uptake and regulation of creatine within human skeletal muscle. This study attempts to characterize the specific variations in creatine receptor activity and concurrent creatine metabolism in human skeletal muscle in response to a regimen of oral creatine supplementation including a one week loading phase, a four week maintenance phase, and a four week washout phase. Supplementation induced significant increments in total body mass (p = 0.03) and lean body mass (p = 0.01). A moderate effect size (d = 0.51) was found for strength increase, which suggests that the study was underpowered to detect a significant difference in strength increase. There appeared to be no effect of supplementation on intramuscular creatine; however, these data were subject to large measurement error and are not likely accurate. There was no apparent effect on creatine transporter mRNA or creatine transporter content when measured after the loading phase, during and after the maintenance phase, and after the washout phase.