Effect of creatine supplementation on oxygen uptake kinetics during submaximal cycle exercise

The purpose of this study was to test the effect of oral creatine (Cr) supplementation on pulmonary oxygen uptake ((V) over dot O-2) kinetics during moderate [below ventilatory threshold (VT)] and heavy (above VT) submaximal cycle exercise. Nine subjects (7 men; means +/- SD: age 28 +/- 3 yr, body mass 73.2 +/- 5.6 kg, maximal (V) over dot O-2 46.4 +/- 8.0 ml.kg(-1). min(-1)) volunteered to participate in this study. Subjects performed transitions of 6-min duration from unloaded cycling to moderate (80% VT; 8-12 repeats) and heavy exercise (50% change; i.e., halfway between VT and maximal (V) over dot O-2; 4-6 repeats), both in the control condition and after Cr loading, in a crossover design. The Cr loading regimen involved oral consumption of 20 g/day of Cr monohydrate for 5 days, followed by a maintenance dose of 5 g/day thereafter. (V) over dot O-2 was measured breath by breath and modeled by using two (moderate) or three (heavy) exponential terms. For moderate exercise, there were no differences in the parameters of the (V) over dot O-2 kinetic response between control and Cr-loaded conditions. For heavy exercise, the time-based parameters of the (V) over dot O-2 response were unchanged, but the amplitude of the primary component was significantly reduced with Cr loading (means +/- SE: control 2.00 +/- 0.12 l/min; Cr loaded 1.92 +/- 0.10 l/min; P < 0.05) as was the end-exercise (V) over do O-2 (control 2.19 +/- 0.13 l/min; Cr loaded 2.12 +/- 0.14 l/min; P < 0.05). The magnitude of the reduction in submaximal (V) over dot O-2 with Cr loading was significantly correlated with the percentage of type II fibers in the vastus lateralis (r = 0.87; P < 0.01; n = 7), indicating that the effect might be related to changes in motor unit recruitment patterns or the volume of muscle activated.