Carnosine is present in high concentrations in mammalian skeletal muscle and is thought to contribute to homeostasis during contractions as a pH buffer and as Ca++ sensitizer. The ingestion of beta-alanine, the ratelimiting precursor amino acid of the dipeptide carnosine (946;-alanyl-L-histidine) has been shown to elevate muscle carnosine content in untrained subjects. The present study aimed to investigate if oral supplementation of betaalanine during 4 weeks could elevate the calf muscle carnosine content in 400m sprint-trained competitive athletes. Second, we investigated if supplementation had an effect on the performance during a 400m indoor race and on the isokinetic and isometric muscle performance and fatigue. Methods: Fifteen male track-and-field athletes with a personal record on 400m below 52s were recruited from Flemish athletics clubs. A placebo-controlled, double-blind study was performed. Subjects were supplemented orally for 4 weeks with 4,8g/day placebo (maltodextrine) or betaalanine (Carnosyn, NAI, San Marcos, USA). Muscle carnosine concentration was determined by the C2-H imidazole peak of the proton NMR spectrum in a single voxel in the soleus and gastrocnemius. The time to complete 400m running was evaluated in an indoor 300m flat athletics track. Subjects also performed an isokinetic test consisting of 5 bouts of 30 maximal voluntary knee extensions on a Biodex isokinetic dynamometer. Additionally, subjects were asked to contract isometrically with their knee extensors at a target torque of 45% of MVC for as long as possible to determine the isometric endurance time. Results: The muscle carnosine content of the soleus increased by 47% (p<0,001) in the beta-alanine group, whereas it remained stable in the placebo group. The increase of carnosine in the gastrocnemius is significantly more pronounced in the beta-alanine group (+37%) than in the placebo group (+16%). A significant pre/post positive effect was observed for the average peak torque in the placebo group for the first two bouts, but not for the subsequent three bouts. Whereas for the beta-alanine group there was a significant pre/post main effect, indicating that average torque was higher is all five bouts post- vs. presupplementation. The knee extensor isometric endurance and the 400m race time were not affected by treatment. Conclusion: It can be concluded from this study that 1) proton NMR spectroscopy can be used to non-invasively and accurately quantify human muscle carnosine content; 2) muscle carnosine content can be substantially elevated by oral beta-alanine supplementation in sprint-trained athletes; 3) muscle carnosine loading significantly attenuates fatigue in repeated bouts of exhaustive dynamic contractions; 4) beta-alanine supplementation does not result in better 400m run performance.
© Copyright 2007 12th Annual Congress of the European College of Sport Science, Jyväskylä, Finland - July 11-14th 2007. Alle Rechte vorbehalten.