We hypothesised that increasing skeletal muscle total creatine (Cr) content through dietary Cr supplementation would result in slower muscle [PCr] kinetics, as assessed using ³¹P- magnetic resonance spectroscopy, following the onset and offset of both moderate-intensity exercise (Mod) and heavy-intensity exercise (Hvy). Seven healthy males (mean ± SD, age 29 ± 6 years) completed a series of square-wave transitions to Mod and Hvy knee-extensor exercise inside the bore of a 1.5 T superconducting magnet both before and after a 5-day period of Cr loading (4 x 5 g/day of creatine monohydrate). Cr supplementation resulted in a ~ 8% increase in the resting muscle PCr/ATP ratio (4.66 ± 0.27 vs. 5.04 ± 0.22; P<0.05), consistent with a significant increase in muscle total Cr content consequent to the intervention. The time constant for muscle [PCr] kinetics was increased following Cr loading for Mod exercise (Con: 15 ± 8 vs. Cr: 25 ± 9 s; P<0.05) and subsequent recovery (Con: 14 ± 8 vs. Cr: 27 ± 8 s; P<0.05), and for Hvy exercise (Con: 54 ± 18 vs. Cr: 72 ± 30 s; P<0.05) but not subsequent recovery (Con: 41 ± 11 vs. Cr: 44 ± 6 s). The magnitude of the increase in [PCr] following Cr-loading was correlated with the extent of the slowing of the [PCr] kinetics (r = 0.39-0.92). These data demonstrate, for the first time in humans, that an increase in muscle [PCr] results in a slowing of [PCr] dynamics in exercise and subsequent recovery and therefore support Meyer's linear model of respiratory control.