J Appl Physiol 92: 2571-2577, 2002.
Effect of creatine supplementation on oxygen uptake kinetics during submaximal cycle exercise
Andrew M. Jones1, Helen Carter2, Jamie S. M. Pringle1, and Iain T. Campbell3
1 Department of Exercise and Sport Science, Manchester Metropolitan University, Alsager ST7 2HL; 2 School of Sport, Exercise and Leisure, University of Surrey Roehampton, London SW15 3SN; and 3 University Department of Anaesthesia, Withington Hospital, Manchester M20 2LR, United Kingdom
The purpose of this study was to test the effect of oral creatine (Cr) supplementation on pulmonary oxygen uptake (O2) 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 O2 46.4 ± 8.0 ml · kg1 · min1) 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 O2; 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. O2 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 O2 kinetic response between control and Cr-loaded conditions. For heavy exercise, the time-based parameters of the O2 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 O2 (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 O2 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.
In conclusion, this study has shown that Cr loading causes a small but significant reduction in O2 during heavy, but not moderate, submaximal exercise, with no change in the primary time constant. The reduction in O2 was present at the end of the primary component and persisted throughout the exercise bout. It is possible that Cr loading influences motor unit recruitment patterns or the volume of muscle mass recruited during heavy submaximal exercise, but additional studies are needed to clarify the mechanism responsible for this effect. |
