Beta-alanine supplementation improves time to exhaustion, but not aerobic capacity, in competitive middle- and long-distance runners.

Background: Beta-alanine (βA) is a non-essential amino acid purportedly used to enhance aerobic exercise performance. While previous research indicates the benefits of βA on time to exhaustion (TTE) and aerobic capacity (VO_2peak) in adults, evidence is lacking in adolescent athletes. Thus, the purpose of this study was to determine the effects of 4 weeks of βA supplementation on aerobic performance in adolescent runners.

Methods: Twenty-seven middle- and long-distance runners (aged 17.36 ± 2.17 years) were randomly divided into a βA or placebo (PL) group (maltodextrin). Subjects performed maximal graded exercise tests (GXT) and submaximal trials (SMT; 80% of VO_2peak for 1500 m) on a treadmill before and after 14 and 28 days of supplementation or PL. Respiratory (V_E) metabolic (VO₂, RER, lactate [La]), and cardiovascular (HR) variables were measured during the GXT and SMT, along with the first (VT1) and second ventilatory threshold (VT2) and TTE monitored during the GXT only. Within- and between-group differences were assessed using a repeated-measures mixed-model analysis of variance.

Results: Findings indicated that despite a trivial increase in VO_2peak over 4 weeks, the βA group increased TTE by 6.5% compared to 1.4% in the PL group (d = 0.46). Additionally, small effects in HR_max, V_E, [La], and TTE were observed between groups favoring βA. Regarding the SMT, both average HR and RER decreased by 4% in the βA group, with no changes for the PL.

Conclusions: Despite no evidence to suggest increases in VO_2peak, practitioners should note that improvements in TTE may be observed after 28 days of βA supplementation in adolescent runners.