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PREEN, D., B. DAWSON, C. GOODMAN, S. LAWRENCE, J. BEILBY, and S. CHING. Effect of creatine loading on long-term sprint exercise performance and metabolism. Med. Sci. Sports Exerc., Vol. 33, No. 5, 2001, pp. 814–821. This study examined whether creatine (Cr) supplementation could enhance long-term repeated-sprint exercise performance of approximately 80 min in duration. Fourteen active, but not well-trained, male subjects initially performed 10 sets of either 5 or 6 × 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, and venous blood was collected preexercise and on four occasions during the exercise challenge. Muscle biopsies (vastus lateralis) were obtained preexercise as well as 0 min and 3 min postexercise. Subjects were then administered either 20 g·d-1 Cr·H2O (N = 7) or placebo (N = 7) for 5 d. Urine samples were collected for each 24 h of the supplementation period. Subjects were then retested using the same procedures as in test 1. Total work done increased significantly (P < 0.05) from 251.7 ± 18.4 kJ presupplementation 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). Work done also improved significantly (P < 0.05) during 6 × 6 s sets with 54-s and 84-s recoveries and approached significance (P = 0.052) in 5 × 6 s sets with 24-s recovery in the Cr condition. Peak power was significantly increased (P < 0.05) in all types of exercise sets after Cr loading. No differences were observed for any performance variables in the placebo group. Resting muscle Cr and PCr concentrations were significantly elevated (P < 0.05) after 5 d of Cr supplementation (Cr: 48.9%; PCr: 12.5%). Phosphocreatine levels were also significantly higher (P < 0.05) immediately and 3 min after the completion of exercise in the Cr condition. The results of this study indicate that Cr ingestion (20 g·day-1 × 5 d) improved exercise performance during 80 min of repeated-sprint exercise, possibly due to an increased TCr store and improved PCr replenishment rate.