Abstract
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−1·day−1) 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−1·day−1) 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 (p = 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% (p = 0.005) and 4.2% to 7.0%, respectively, during the last three sprints (p = 0.005 to 0.001). The reduction in speed within each sprint was also blunted by 16.2% (p = 0.003) following Cr supplementation. Plasma ammonia decreased by 20.1% (p = 0.037) after Cr supplementation, despite the increase in performance. VO2 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.
Highlights
In several individual and team sports, training schedules include the performance of repeated sprints once or twice per week in order to improve speed and the ability to repeat intense efforts with short recovery intervals [1–3]
Only a main effect of sprint number was found for blood La during the speed lactate test (p < 0.001, η2 = 0.87, Table 1)
While the three-way analysis of variance (ANOVA) for MPO/kg achieved during the first 5 s of each sprint did not show any interactions, but rather only a main effect of sprint number (p < 0.001, η2 = 0.89), the three-way ANOVA for MPO/kg during the last 5 s of each sprint showed a pre–post x group interaction (p = 0.010, η2 = 0.38), with the post hoc test revealing an average of 4.5% increase in mean power output during the last 5 s of the six sprints after Cr supplementation (p = 0.005; Figure 2C,D)
Summary
In several individual and team sports, training schedules include the performance of repeated sprints once or twice per week in order to improve speed and the ability to repeat intense efforts with short recovery intervals [1–3]. The rapid but incomplete rates of muscle PCr resynthesis during recovery intervals commonly used in sports practice (i.e., 30 s to 3 min) [11] make it very tempting to attempt to alter either PCr resting levels and/or the rate of PCr resynthesis This is especially important, as the inability to maintain high power output during all-out exercise, i.e., fatigue, has been associated with decreased phosphocreatine levels [8,12], while the rate of recovery mirrors that of power output during the initial seconds of a repeated bout [6]. Studies [8] reported that phosphocreatine (PCr) is the single anaerobic source during the last of a series of ten 6 s cycling sprints with 30 s rest [6,13] This would suggest that a possibly faster PCr resynthesis would improve performance towards the last bouts. These findings emphasise PCr as being central for maintaining a high ATP-to-adenosine diphosphate (ADP) ratio and a high-power output
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