Abstract
Purpose: To investigate the influence of β-alanine (BA) supplementation on muscle carnosine content, muscle pH and the power-duration relationship (i.e., critical power and W′).Methods: In a double-blind, randomized, placebo-controlled study, 20 recreationally-active males (22 ± 3 y, V°O2peak 3.73 ± 0.44 L·min−1) ingested either BA (6.4 g/d for 28 d) or placebo (PL) (6.4 g/d) for 28 d. Subjects completed an incremental test and two 3-min all-out tests separated by 1-min on a cycle ergometer pre- and post-supplementation. Muscle pH was assessed using 31P-magnetic resonance spectroscopy (MRS) during incremental (INC KEE) and intermittent knee-extension exercise (INT KEE). Muscle carnosine content was determined using 1H-MRS.Results: There were no differences in the change in muscle carnosine content from pre- to post-intervention (PL: 1 ± 16% vs. BA: −4 ± 25%) or in muscle pH during INC KEE or INT KEE (P > 0.05) between PL and BA, but blood pH (PL: −0.06 ± 0.10 vs. BA: 0.09 ± 0.13) during the incremental test was elevated post-supplementation in the BA group only (P < 0.05). The changes from pre- to post-supplementation in critical power (PL: −8 ± 18 W vs. BA: −6 ± 17 W) and W′ (PL: 1.8 ± 3.3 kJ vs. BA: 1.5 ± 1.7 kJ) were not different between groups. No relationships were detected between muscle carnosine content and indices of exercise performance.Conclusions: BA supplementation had no significant effect on muscle carnosine content and no influence on intramuscular pH during incremental or high-intensity intermittent knee-extension exercise. The small increase in blood pH following BA supplementation was not sufficient to significantly alter the power-duration relationship or exercise performance.
Highlights
The critical power (CP) model of high-intensity exercise performance is defined by two parameters: the CP, representing the highest sustainable rate of oxidative phosphorylation, and the W′, notionally a fixed energy store derived principally from substrate-level phosphorylation (Monod and Scherrer, 1965; Moritani et al, 1981; Poole et al, 1988; Jones et al, 2008, 2010)
Baseline muscle carnosine content was determined using 1H magnetic resonance spectroscopy (1H-MRS) which was followed by incremental knee extension exercise (INC KEE) with muscle metabolic changes assessed via 31P magnetic resonance spectroscopy (31P-MRS)
There were no significant differences in physical characteristics or physiological/fitness measures at baseline between the PL and BA supplementation groups (Table 1)
Summary
The critical power (CP) model of high-intensity exercise performance is defined by two parameters: the CP, representing the highest sustainable rate of oxidative phosphorylation, and the W′, notionally a fixed energy store derived principally from substrate-level phosphorylation (Monod and Scherrer, 1965; Moritani et al, 1981; Poole et al, 1988; Jones et al, 2008, 2010). Consistent with the notion that metabolic acidosis contributes to muscular fatigue, improved muscle H+ efflux is related to enhanced intense exercise performance (Hostrup and Bangsbo, 2017). Other studies have shown no significant effect of BA supplementation on performance (Sweeney et al, 2010; Saunders et al, 2012a; Ducker et al, 2013; Jagim et al, 2013), despite subjects following an appropriate supplementation strategy (Hobson et al, 2012) and completing a test ostensibly >CP that would be expected to result in a large decline in muscle pH (Bogdanis et al, 1998; Vanhatalo et al, 2016). Despite possible ergogenic effects of BA supplementation being attributed to enhanced intramuscular buffering capacity, no study has assessed differences in muscle pH during exercise in humans following BA supplementation. Despite possible ergogenic effects of BA supplementation being attributed to enhanced intramuscular buffering capacity, no study has assessed differences in muscle pH during exercise in humans following BA supplementation. 31P-MRS affords the opportunity to non-invasively assess muscle pH during exercise with a high temporal resolution
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