title: Oral creatine supplementation decreases plasma markers of adenine nucleotide degradation during a 1-h cycle test.
abstract: We investigated the effect of oral creatine supplementation (20 g d(-1) for 7 days) on metabolism during a 1-h cycling performance trial. Twenty endurance-trained cyclists participated in this double-blind placebo controlled study. Five days after familiarization with the exercise test, the subjects underwent a baseline muscle biopsy. Thereafter, a cannula was inserted into a forearm vein before performing the baseline maximal 1-h cycle (test 1 (T1)). Blood samples were drawn at regular intervals during exercise and recovery. After creatine (Cr) loading, the muscle biopsy, 1-h cycling test (test 2 (T2)) and blood sampling were repeated. Resting muscle total creatine (TCr), measured by high performance liquid chromatography, was increased (P < 0.001) in the creatine group from 123.0 +/- 3.8 - 159.8 +/- 7.9 mmol kg(-1) dry wt, but was unchanged in the placebo group (126.7 +/- 4.7 - 127.5 +/- 3.6 mmol kg(-1) dry wt). The extent of Cr loading was unrelated to baseline Cr levels (r=0.33, not significant). Supplementation did not significantly improve exercise performance (Cr group: 39.1 +/- 0.9 vs. 39.8 +/- 0.8 km and placebo group: 39.3 +/- 0.8 vs. 39.2 +/- 1.1 km) or change plasma lactate concentrations. Plasma concentrations of ammonia (NH(3)) (P < 0.05) and hypoxanthine (Hx) (P < 0.01) were lower in the Cr group from T1 to T2. Our results indicate that Cr supplementation alters the metabolic response during sustained high-intensity submaximal exercise. Plasma data suggest that nett intramuscular adenine nucleotide degradation may be decreased in the presence of enhanced intramuscular TCr concentration even during submaximal exercise.
authors.affiliation: MRC/UCT Bioenergetics of Exercise Research Unit, Department of Physiology, University of Cape Town Medical School, Observatory, 7925, South Africa.
authors.forename: B M
authors.initials: BM
authors.lastname: Bellinger
authors.forename: A
authors.initials: A
authors.lastname: Bold
authors.forename: G R
authors.initials: GR
authors.lastname: Wilson
authors.forename: T D
authors.initials: TD
authors.lastname: Noakes
authors.forename: K H
authors.initials: KH
authors.lastname: Myburgh
mesh_terms: D000227:Adenine Nucleotides / Q000378:metabolism*; D000641:Ammonia / Q000097:blood; D002851:Chromatography, High Pressure Liquid; D003404:Creatinine / Q000008:administration & dosage* / Q000097:blood; D019587:Dietary Supplements; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D019271:Hypoxanthine / Q000097:blood; D019344:Lactic Acid / Q000097:blood; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism; D014527:Uric Acid / Q000097:blood
chemical_list: D000227:Adenine Nucleotides; D014527:Uric Acid; D019271:Hypoxanthine; D019344:Lactic Acid; D000641:Ammonia; D003404:Creatinine