Creatine feeding does not enhance intramyocellular glycogen concentration during carbohydrate loading: an in vivo study by31P-and13C-MRS

The main aim of this study was to examine the hypothesis that creatine (Cr) feeding enhances myocellular glycogen storage in humans undergoing carbohydrate loading. Twenty trained male subjects were randomly assigned to have their diets supplemented daily with 252 g of glucose polymer (GP) and either 21 g of Cr (CRGP, n=10) or placebo (PL-GP, n=10) for 5 days. Changes in resting myocellular glycogen and phosphocreatine (PCr) were determined with Magnetic Resonance Spectroscopy (13C- and31P-MRS, respectively). After CR-GP, the levels of intramyocellular glycogen increased from 147±13 (standard error) mmol·(kg wet weight)−1) to 182±17 mmol·(kg wet weight)−1, while it increased from 134±17 mmol·(kg wet weight)− to 182±17 mmol·(kg wet weight)−1 after PL-GP; the increments in intramyocellular glycogen concentrations were not statistically different. The increment in the PCr/ATP ratio after CR-GP (+0.20±0.12) was significantly different compared to PL-GP (−0.34±0.16) (p<0.05). The present results do not support the hypothesis that Cr loading increases muscle glycogen storage.