Chronic Muscle Inactivity Does Not Affect Muscle Carnosine Loading Induced By Beta-Alanine Supplementation

PURPOSE: to study the impact of the extremes of muscle activity and inactivity on muscle carnosine content (Mcarn) and Mcarn loading in response to beta-alanine supplementation. METHODS: 16 trained male with spinal cord injury (SCI) (ASIA scale: AIS A or AIS B) were divided into 2 groups: beta-alanine (BA) (N = 11) and placebo (PL) (N = 5). Muscle biopsies samples were obtained from active deltoid and paralysed vastus lateralis at baseline and after 28 days of beta-alanine supplementation (6.4 g‧day-1). Unpaired t-tests were applied to compare Mcarn at baseline and the absolute pre-post change in vastus lateralis and deltoid. Mixed model was used to compare Mcarn values within- and between-subjects. RESULTS: (mean±SD): Baseline Mcarn concentration in vastus lateralis was significantly higher than in deltoid (32.0±12 vs. 20.5±6.1 mmol‧kg-1 dry muscle; p=0.02). Absolute changes in Mcarn was significantly higher in the BA group in comparison with PL for both vastus lateralis (BA: 17.6±10.4 mmol‧kg-1 dry muscle; PL: 2.5±2.3 mmol‧kg-1 dry muscle; p=0.002) and deltoid (BA: 15.7±6.8 mmol‧kg-1 dry muscle; PL: 1.4±2.7 mmol‧kg-1 dry muscle; p<0.001). Absolut changes in Mcarn following BA supplementation between inactive vastus lateralis and active deltoid was not different (vastus lateralis: 17.6±10.4; deltoid: 15.7±6.8 mmol‧kg-1 dry muscle; p=0.6). CONCLUSION: chronic muscle inactivity due to paralysis in SCI does not affect Mcarn at baseline and does not affect Mcarn loading in response to BA supplementation. These results suggest that muscle activity or training status does not influence Mcarn synthesis capacity in response to beta-alanine supplementation. Supported by CEPID-Redoxoma (São Paulo Research Foundation FAPESP: Proc. 2013/07937-8, and CAPES- PROEX 1888/2016), and FAPESP thematic grant (13/14746-4).