β-alanine supplementation improves isometric endurance of the knee extensor muscles

BACKGROUND: We examined the effect of four weeks of β-alanine supplementation on isometric endurance of the knee extensors at 45% maximal voluntary isometric contraction (MVIC). METHODS: Thirteen males (age 23 ± 6 y; height 1.80 ± 0.05 m; body mass 81.0 ± 10.5 kg), matched for pre-supplementation isometric endurance, were allocated to either a placebo (n = 6) or β-alanine (n = 7; 6.4 g·d(-1) over 4 weeks) supplementation group. Participants completed an isometric knee extension test (IKET) to fatigue, at an intensity of 45% MVIC, before and after supplementation. In addition, two habituation tests were completed in the week prior to the pre-supplementation test and a further practice test was completed in the week prior to the post-supplementation test. MVIC force, IKET hold-time, and impulse generated were recorded. RESULTS: IKET hold-time increased by 9.7 ± 9.4 s (13.2%) and impulse by 3.7 ± 1.3 kN·s(-1) (13.9%) following β-alanine supplementation. These changes were significantly greater than those in the placebo group (IKET: t((11)) = 2.9, p ≤0.05; impulse: t((11)) = 3.1, p ≤ 0.05). There were no significant changes in MVIC force in either group. CONCLUSION: Four weeks of β-alanine supplementation at 6.4 g·d(-1) improved endurance capacity of the knee extensors at 45% MVIC, which most likely results from improved pH regulation within the muscle cell as a result of elevated muscle carnosine levels.