Kinetics of Muscle Carnosine Decay after β-alanine Supplementation: A 16-Week Washout Study.

PURPOSE To describe the kinetics of carnosine washout in human skeletal muscle over 16 weeks. METHODS Carnosine washout kinetics were studied in fifteen young, physically-active omnivorous men randomly assigned to take 6.4 g·d of β-alanine (n=11) or placebo (PL, n=4) for 8 weeks. Muscle carnosine content (M-Carn) was determined before (PRE), immediately after (POST) and 4, 8, 12 and 16 weeks after supplementation. High-intensity exercise tests were performed at these same time points. Linear and exponential models were fitted to the washout data and the leave-one-out method was used to select the model with the best fit for M-Carn decay data. Repeated measures correlation analysis was used to assess the association between changes in M-Carn and changes in performance. RESULTS M-Carn increased from PRE to POST in the β-alanine group only (+91.1±29.1%; PL:+0.04±10.1%; p<0.0001). M-Carn started to decrease after cessation of β-alanine supplementation and continued to decrease until week 16 (POST4:+59±40%; POST8:+35±39%; POST12:+18±32%; POST16:-3±24% of PRE M-Carn). From week 12 onwards, M-Carn was no longer statistically different from PRE. Both linear and exponential models displayed very similar fit and could be used to describe carnosine washout, although the linear model presented a slightly better fit. The decay in M-Carn was mirrored by a similar decay in high-intensity exercise tolerance; M-Carn was moderately and significantly correlated with TWD (r=0.505; p=0.032) and TTE (r=0.72; p<0.001). CONCLUSION Carnosine washout takes 12-16 weeks to complete, and it can be described either by linear or exponential curves. Changes in M-Carn appear to be mirrored by changes in high-intensity exercise tolerance. This information can be used to optimise β-alanine supplementation strategies.