Effect of 28 days of creatine ingestion on muscle metabolism and performance of a simulated cycling road race.

Purpose: The effects of creatine supplementation on muscle metabolism and exercise performance during a simulated endurance road race was investigated.

Methods: Twelve adult male (27.3 +/- 1.0 yr, 178.6 +/- 1.4 cm, 78.0 +/- 2.5 kg, 8.9 +/- 1.1 %fat) endurance-trained (53.3 +/- 2.0 ml* kg-1* min-1, cycling ~160 km/wk) cyclists completed a simulated road race on a cycle ergometer (Lode), consisting of a two-hour cycling bout at 60% of peak aerobic capacity (VO2peak) with three 10-second sprints performed at 110% VO2 peak every 15 minutes. Cyclists completed the 2-hr cycling bout before and after dietary creatine monohydrate or placebo supplementation (3 g/day for 28 days). Muscle biopsies were taken at rest and five minutes before the end of the two-hour ride.

Results: There was a 24.5 +/- 10.0% increase in resting muscle total creatine and 38.4 +/- 23.9% increase in muscle creatine phosphate in the creatine group (P < 0.05). Plasma glucose, blood lactate, and respiratory exchange ratio during the 2-hour ride, as well as VO2 peak, were not affected by creatine supplementation. Submaximal oxygen consumption near the end of the two-hour ride was decreased by approximately 10% by creatine supplementation (P < 0.05). Changes in plasma volume from pre- to post-supplementation were significantly greater in the creatine group (+14.0 +/- 6.3%) than the placebo group (-10.4 +/- 4.4%; P < 0.05) at 90 minutes of exercise. The time of the final sprint to exhaustion at the end of the 2-hour cycling bout was not affected by creatine supplementation (creatine pre, 64.4 +/- 13.5s; creatine post, 88.8 +/- 24.6s; placebo pre, 69.0 +/- 24.8s; placebo post 92.8 +/- 31.2s: creatine vs. placebo not significant). Power output for the final sprint was increased by ~33% in both groups (creatine vs. placebo not significant).

Conclusions: It can be concluded that although creatine supplementation may increase resting muscle total creatine, muscle creatine phosphate, and plasma volume, and may lead to a reduction in oxygen consumption during submaximal exercise, creatine supplementation does not improve sprint performance at the end of endurance cycling exercise.