Abstract
BackgroundWe examined the effect of four weeks of β-alanine supplementation on isometric endurance of the knee extensors at 45% maximal voluntary isometric contraction (MVIC).MethodsThirteen 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.ResultsIKET 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.ConclusionFour 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.
Highlights
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)
In this study we show the effect of 4 weeks of β-alanine supplementation on isometric endurance of the knee extensors at 45% MVIC and demonstrate a 13.2% increase in isometric endurance and a 13.9% increase in impulse
The increase in H+ is of the same order as the estimated increase in buffering capacity from the expected increase in muscle carnosine levels, brought about by the programme of β-alanine supplementation (i.e., 6.4 gÁd-1 β-alanine or 179.2 g in total)
Summary
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). High-intensity exercise is associated with the formation and net accumulation of carboxylic acid groups, principally in the form of the lactate anion (Lac-). Physicochemical buffers need to be present in high concentrations in the muscle and require a pKa that is within the exercise-induced pH transit range. Carnosine (β-alanyl-L-histidine) is a cytoplasmic dipeptide found in high concentrations in skeletal muscle [11] and has a pKa of 6.83 for the imidazole ring, which makes it a suitable buffer over the physiological pH range [12,13]. Carnosine is formed by bonding histidine and β-alanine in a reaction catalysed by carnosine synthase, in humans, formation of carnosine in the skeletal muscle is limited by the availability of βalanine [14]
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