Effects of l-citrulline supplementation on nitric oxide and antioxidant markers after high-intensity interval exercise in young men: a randomised controlled trial

Abstract

Abstract l-Citrulline (l-Cit) is a non-essential amino acid that stimulates nitric oxide (NO) production and improves exercise performance by reducing muscle damage indices; however, the direct benefits of l-Cit on antioxidant markers are unclear. The aim of this study was to examine antioxidant responses to high-intensity interval exercise following acute l-Cit supplementation. Nine young men (21 (sd 1) years) participated in a double-blind crossover study in which they received 12 g of l-Cit and placebo (PL) an hour prior to high-intensity interval exercise on two occasions, separated by a 7-d washout period. Blood samples were obtained before (PRE), immediately after (IP), 10 (10P) and 30 min after exercise (30P) from the cubital vein using standard procedures. Serum concentrations of superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT) and NO metabolites (NOx) were measured. The exercise protocol significantly elevated SOD (P = 0·01) and GPx (P = 0·048) from PRE to 10P in the l-Cit group with greater changes than the PL group. CAT concentrations increased IP (P = 0·014) and remained elevated at 10P (P = 0·03) and 30P (P = 0·015) in both the l-Cit and PL conditions. NOx concentrations increased IP (P = 0·05) in the l-Cit group with greater changes than PL group in PRE to IP, PRE to 10P and PRE to 30P (P < 0·05). Our data indicate that l-Cit supplementation (single 12 g dose pre-exercise) induces improvements in antioxidant markers following a session of high-intensity interval exercise in young men.