| Summary: | The aim of the present study was to examine the effects of creatine (Cr) supplementation on power output during repeated sprints on a non-motorized treadmill. Sixteen recreationally active males volunteered for this study (age 25.5 ± 4.8 y, height 179 ± 5 cm, body mass 74.8 ± 6.8 kg). All participants received placebo supplementation (75 mg of glucose·kg<sup>−1</sup>·day<sup>−1</sup>) for 5 days and then performed a baseline repeated sprints test (6 × 10 s sprints on a non-motorised treadmill). Thereafter, they were randomly assigned into a Cr (75 mg of Cr monohydrate·kg<sup>−1</sup>·day<sup>−1</sup>) or placebo supplementation, as above, and the repeated sprints test was repeated. After Cr supplementation, body mass was increased by 0.99 ± 0.83 kg (<i>p =</i> 0.007), peak power output and peak running speed remained unchanged throughout the test in both groups, while the mean power output and mean running speed during the last 5 s of the sprints increased by 4.5% (<i>p</i> = 0.005) and 4.2% to 7.0%, respectively, during the last three sprints (<i>p =</i> 0.005 to 0.001). The reduction in speed within each sprint was also blunted by 16.2% (<i>p =</i> 0.003) following Cr supplementation. Plasma ammonia decreased by 20.1% (<i>p</i> = 0.037) after Cr supplementation, despite the increase in performance. VO<sub>2</sub> and blood lactate during the repeated sprints test remained unchanged after supplementation, suggesting no alteration of aerobic or glycolytic contribution to adenosine triphosphate production. In conclusion, Cr supplementation improved the mean power and speed in the second half of a repeated sprint running protocol, despite the increased body mass. This improvement was due to the higher power output and running speed in the last 5 s of each 10 s sprint.
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