The effect of β-alanine supplementation during high-intensity interval training on repeated sprint ability performance and neuromuscular fatigue.

The study investigated the influence of β-Alanine supplementation during a high-intensity interval training (HIIT) program on repeated sprint ability (RSA) performance. This study was randomized, double-blinded and placebo-controlled. Eighteen men performed an incremental running test until exhaustion (T_INC) at baseline and followed by 4-week HIIT (10×1-min runs 90% maximal T_INC velocity [1-min recovery]). Then, participants were randomized into 2 groups and performed a 6-week HIIT associated with supplementation of 6.4g·day^-1 of β-Alanine (Gβ) or dextrose (Placebo group; GP). Pre and Post 6-week HIIT+supplementation, participants performed the following tests: 1) T_INC; 2) supramaximal running test; and 3) 2×6×35-m sprints (RSA). Before and immediately after RSA, neuromuscular function was assessed by vertical jumps, maximal isometric voluntary contractions of knee extension and neuromuscular electrical stimulations. Muscle biopsies were performed to determine muscle carnosine content, muscle buffer capacity in vitro (βm_invitro) and content of phosphofructokinase (PFK), monocarboxylate transporter 4 (MCT4) and hypoxia-inducible factor-1α (HIF-1α). Both groups showed a significant time-effect for maximal oxygen uptake (Gβ:6.2±3.6% and GP:6.5±4.2%; p>0.01); only Gβ showed a time effect for total (-3.0±2.0%; p=0.001) and best (-3.3±3.0%; p=0.03) RSA times. A group-by-time interaction was shown after HIIT+Supplementation for muscle carnosine (Gβ: 34.4±2.3mmol.kg^-1dm and GP: 20.7±3.0mmol.kg^-1dm; p=0.003) and neuromuscular voluntary activation after RSA (Gβ:87.2±3.3% and GP:78.9±12.4%; p=0.02). No time effect or group-by-time interaction were shown for supramaximal running test performance, βminvitro and content of PFK, MCT4 and HIF-1α. In summary, β-Alanine supplementation during HIIT increased muscle carnosine and attenuated neuromuscular fatigue, which may contribute to an enhancement of RSA performance.