Acute heat stress amplifies exercise‐induced metabolomic perturbations and reveals variation in circulating amino acids in endurance‐trained males

Abstract Using untargeted metabolomics, we aimed to characterise the systemic impact of environmental heat stress during exercise. Twenty‐three trained male triathletes ( = 64.8 ± 9.2 ml kg min −1 ) completed a 30‐min exercise test in hot (35°C) and temperate (21°C) conditions. Venous blood samples were collected immediately pre‐ and post‐exercise, and the serum fraction was assessed via untargeted 1 H‐NMR metabolomics. Data were analysed via uni‐ and multivariate analyses to identify differences between conditions. Mean power output was higher in temperate (231 ± 36 W) versus hot (223 ± 31 W) conditions ( P < 0.001). Mean heart rate (temperate, 162 ± 10 beats min −1 , hot, 167 ± 9 beats min −1 , P < 0.001), peak core temperature ( T rec ), core temperature change (Δ T rec ) ( P < 0.001) and peak rating of perceived exertion ( P = 0.005) were higher in hot versus temperate conditions. Change in metabolite abundance following exercise revealed distinct clustering following multivariate analysis. Six metabolites increased (2‐hydroxyvaleric acid, acetate, alanine, glucarate, glucose, lactate) in hot relative to temperate ( P < 0.05) conditions. Leucine and lysine decreased in both conditions but to a greater extent in temperate conditions ( P < 0.05). Citrate ( P = 0.04) was greater in temperate conditions whilst creatinine decreased in hot conditions only ( P > 0.05). Environmental heat stress increased glycolytic metabolite abundance and led to distinct alterations in the circulating amino acid availability, including increased alanine, glutamine, leucine and isoleucine. The data highlight the need for additional exercise nutrition and metabolism research, specifically focusing on protein requirements for exercise under heat stress.