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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 · kg
1 · 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.
economy; steady state; fiber type
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