Long-Term Effect of Combined Citrulline and Nitrate-Rich Beetroot Extract Supplementation

Overview

Citrulline (CIT) and nitrate-rich beetroot extract (BEET) are widely studied ergogenic aids. However, both supplements have been studied in sort-term and isolated. To the best of the authors' knowledge, the effects of combining both supplements on exercise-induced muscle damage (EIMD) and hormone status have not been investigated to date. Therefore, the main purpose of this study was to determine the effect and degree of potentiation of the long-term (9 weeks) mixture of 3 g/day of CIT plus 2.1 g/day of BEET (300 mg/day of NIT) supplementation on EIMD markers (urea, creatinine, AST, ALT, GGT, LDH and CK) and anabolic/catabolic hormone status (testosterone, cortisol and Testosterone cortisol ratio (T/C)) in male trained triathletes. This study was a double-blind, placebo-controlled trial where participants (n = 32) were randomized into 4 different groups: placebo group (PLG; n = 8), CIT group (CITG; 3 g/day of CIT; n = 8), BEET group (BEETG; 2.1 g/day of BEET (300 mg/day of NIT) ; n = 8) and CIT-NIT group (CIT-BEETG; 3 g/day of CIT plus 2.1 g/day of BEET (300 mg/day of NIT); n = 8). Blood samples were collected from all participants at baseline (T1) and after 9 weeks of supplementation (T2).

Triathlon is an endurance sport in which athletes compete sequentially in swimming, cycling and running. Prolonged and strenuous training combined with insufficient recovery can produce muscular and metabolic stress, resulting in structural and functional damage to the musculoskeletal system leading to a fatigue status, which results in decreased athletic performance. As a consequence of this type of combined exercise, there are also alterations in biochemical markers of exercise-induced muscle damage (EIMD) as well as anabolic/catabolic hormones. Therefore, their analysis is useful in determining the balance between training loads and recovery. In this sense, it is essential to include different strategies to reduce or prevent EIMD, which delay or reduce muscle fatigue and improve sports performance. One of these strategies is the use of different ergogenic aids such as L-citrulline (CIT) and nitrates (NIT) which have been proposed as both substances produce an increase in nitric oxide (NO).