Effect of creatine loading on long-term sprint exercise performance and metabolism

Purpose: This study examined whether creatine (Cr) supplementation could en hance long-term repeated-sprint exercise performance of approximately 80 mi n in duration. Methods: Fourteen active, but not will-trained. male subject s initially performed 10 sets of either 5 or 6 x 6 s maximal bike sprints, with varying recoveries (24, 54, or 84 s between sprints) over a period of 80 min. Work done (kJ) and peak power (W) were recorded for each sprint, an d venous blood was collected preexercise and an four occasions during the e xercise challenge, Muscle biopsies (vastus lateralis) were obtained preexer cise as well as 0 min and 3 min postexercise. Subjects were then administer ed either 20 g.d(-1) Cr.H2O (N = 7) or placebo (N = 7) for 5 d. Urine sampl es were collected for each 24 h of the supplementation period. Subjects wer e then retested using the same procedures as in test 1, Results: Total work done increased significantly (P < 0.05) from 251.7 +/- 18.4 kJ presuppleme ntation to 266.9 +/- 19.3 kJ (6% increase after Cr ingestion. No change was observed for the placebo group (254.0 +/- 10.4 kJ to 252.3 +/- 9.3 kJ). Wo rk done also improved significantly (P < 0.05) during 6 x 6 s sets with 54- s and 84-s recoveries and approached significance (P = 0.052) in 5 x 6 s se ts with 24-s recovery in the Cr condition. Peak power was significantly inc reased (P < 0.05) in all types of exercise sets after Cr loading. No differ ences were observed for any performance variables in the placebo group. Res ting muscle Cr and PCr concentrations were significantly elevated (P < 0.05 after 5 d of Cr supplementation (Cr: 48.9%: PCr: 12.5%). Phosphocreatine l evels were also significantly higher (P < 0.05) immediately arid 3 min afte r the completion of exercise in the Ci condition. Conclusion: The results o f this study indicate that Cr ingestion (20 g.day(-1) x 5 d) improved exerc ise performance during 80 min of repeated-sprint exercise. possibly due to an increased TCr store and improved PCr replenishment rate.