Creatine supplementation and dynamic high-intensity intermittent exercise

Two intermittent high-intensity exercise protocols were performed before and after the administration of either creatine or a placebo, and performance characteristics and selected physiological responses were studied. Each exercise protocol consisted of 10 6-s bouts of high-intensity cycling at 2 exercise intensities (130 rev/min [EX130]: ∼820 W and 140 rev/min [EX140)]: ∼ 880 W) so that in EX130 the same amount of exercise was performed before and after the administration period, whereas an exercise intensity in EX140 was chosen to induce fatigue over the 10 exercise bouts. Sixteen healthy male subjects were randomly assigned to the 2 experimental groups. A double-blind design was used in this study. There were no significant changes in the placebo group for any of the measured parameters. Performance towards the end of each exercise bout in EX140 was enhanced following creatine supplementation, as shown by a smaller decline in work output from baseline along the 10 trials. Although more work was performed in EX140, after vs before the administration period, blood lactate accumulation decreased (mean and SEM), from 10.8 (0.5) to 9.1 (0.8) mmol·l−1 and plasma accumulation of hypoxanthine decreased from 21.1 (0.4) to 16.7 (0.8) μmol·l−1, but there was no change in oxygen uptake measured during 3 exercise and recovery periods [3.18 (0–1) vs 3.14 (0.1) l·min−1]. In EX130 blood lactate accumulation decreased, from 7.0 (0.5) to 5.1 (0.5) mmol·l−1, and oxygen uptake was also lower, decreasing from 2.84 (0.1) to 2.78 (0.1) l·min−1. A significant increase in body mass (11 kg: range 0.3 to 2.5 kg) was found in the creatine group. The mechanism responsible for the improved performance with creatine supplementation are postulated to be both a higher initial creatine phosphate content availability and an increased rate of creatine phosphate resynthesis during recovery periods. The lower blood lactate and hypoxanthine accumulation can also be explained by these mechanisms.