Effect of creatine supplementation on muscle metabolic response to a maximal treadmill exercise test in Standardbred horses

The aim of the present study was to investigate the effect of creatine (Cr) supplementation on muscle metabolic response in connection with a maximal treadmill exercise test, known to cause a marked anaerobic metabolic respon se and adenine nucleotide degradation. First, 6 Standardbred trotters perfo rmed a standardised maximal exercise test until fatigue (baseline test). Th e test used was an inclined incremental treadmill test in which the speed w as increased by 1 m/s, starting at 7 m/s, every 60 s until the horse could no longer keep pace with the treadmill. After this baseline test, the horse s were separated into 2 equal groups. One half received a dose of 25 g crea tine monohydrate twice daily, and the other group were given the same dose of lactose (placebo). The supplementation period was 6.5 days, after which the maximal treadmill exercise test was performed again. A washout period o f 14 days was allowed before treatments were switched between groups and a new supplementation period started. After this second supplementation perio d a new maximal exercise test was performed. After supplementation with cre atine or placebo, horses were stopped after performing the same number of s peed steps and duration of exercise as they had in the baseline test. Blood samples for analysis of plasma lactate, creatine (Cr), creatinine, hypoxan thine, xanthine and uric acid concentrations were collected at rest, during each speed step and during recovery. The total blood volume (TBV) was also determined. Muscle biopsies for analysis of muscle metabolites (adenosine triphosphate [ATP], adenosine diphosphate [ADP], adenosine monophosphate [A MP], inosine monophosphate [IMP], creatine phosphate [CP], lactate [La] and glycogen) were taken at rest, immediately post exercise and after 15 min r ecovery. The results showed no significant increase in plasma Cr or muscle total creatine concentration (TCr) after supplementation with Cr. At the en d of exercise ATP and CP concentrations had decreased and IMP and lactate c oncentrations increased in muscle in all groups. Plasma lactate concentrati on increased during exercise and recovery and plasma uric acid concentratio n increased during recovery in all groups. No influence could be found in T BV after supplementation with creatine. These results show that creatine su pplementation in the dosage used in this study had no influence on muscle m etabolic response or TBV.