Effects of β-alanine supplementation and multicomponent circuit training on aerobic capacity, performance, and plasma metabolites in untrained young adults: a randomized, placebo-controlled trial with double-blind supplementation

Chronic β-alanine supplementation increases skeletal muscle carnosine and may enhance high-intensity exercise performance. However, evidence regarding its effects in untrained individuals, particularly females, and in combination with multicomponent training remains limited. This randomized controlled trial investigated the effects of β-alanine supplementation combined with training on physical performance and plasma carnosine-related metabolites in untrained young adults. In this randomized, placebo-controlled trial with double-blind supplement allocation, 46 healthy untrained young adults were randomized, and 43 commenced and completed the six-week intervention (β-alanine [BA], n = 23; placebo [PL], n = 20; age: 22.3 ± 1.7 years). Participants received β-alanine (50 mg/kg/day) or placebo during progressive multicomponent circuit training. Anthropometry, shuttle-run performance, estimated VO₂max, maximal voluntary isometric knee-extension torque, forced vital capacity (FVC), blood lactate responses, and plasma β-alanine, histidine, and carnosine concentrations were assessed before and after the intervention. Outcomes were analysed using 2 × 2 mixed-model ANOVA. Complete outcome data were available for 43 participants, except for shuttle-run performance and estimated VO₂max, which were analysed in 41 participants (BA, n = 21; PL, n = 20). No significant time × treatment interactions were observed for maximal voluntary isometric knee-extension torque, estimated VO₂max, body composition, blood lactate accumulation, or FVC. Training significantly improved shuttle-run performance and estimated VO₂max over time (both p < 0.001), without additional effects of β-alanine supplementation (interaction p = 0.125 and p = 0.073, respectively). Significant time × treatment interactions were observed for plasma histidine and post-exercise plasma carnosine concentrations ( p < 0.05), while plasma β-alanine concentrations were affected by both training and supplementation. In untrained young adults, six weeks of multicomponent circuit training resulted in improvements in selected physical and physiological outcomes, whereas β-alanine supplementation increased post-exercise plasma carnosine concentrations without providing additional performance benefits beyond training alone. These findings highlight the importance of training-related adaptations and suggest that changes in plasma carnosine should not necessarily be interpreted as evidence of functional improvement. ClinicalTrials.gov, NCT07404540; retrospectively registered on 29 January 2026 (first publicly posted on 11 February 2026).