Abstract

Ingestion of Citrulline Malate (CM) has been shown to improve exercise with beneficial effects reported during strength-based assessments and time trial performance (Suzuki et al. [2016]. Journal of The International Society of Sports Nutrition, 13). CM has been reported to increase plasma arginine availability and subsequent nitric oxide (NO) production, leading to increased blood flow. Citrulline in particular accelerates the ureagenesis cycle resulting in the removal of ammonium while Malate is essential for oxidative metabolism which regulates skeletal muscle functions including glucose and fatty acid oxidation. Despite this, the metabolic influence of CM has received little attention in the literature. Much of the current literature has primarily focused on performance outcomes during high intensity exhaustive exercise. As such, the purpose of this study was to investigate the effects of CM on substrate utilisation during a low-moderate cardiorespiratory exercise test. This study used a randomised controlled cross-over design and adopted double-blind procedures. Following institutional ethical approval, nine healthy, and active participants (4 males, 5 females) were recruited for the study with only eight completing both trials. Over a period of 38 days, participants completed one familiarisation and two experimental trials, each of which was separated by at least three days. In the experimental trials, participants consumed either CM (3×1000mg) or PLA (3×100% lactose) 60 minutes prior to completing a modified Bruce treadmill protocol, with increases in speed and gradient every 3 minutes until 85% of maximum heart rate (HR) was achieved. HR and breath-by-breath values for oxygen uptake, respiratory exchange ratio and ventilation were obtained at rest and during the final 30s of each 3-minute stage. RPE (Borg 6-20) was also recorded at the end of each stage. Respiratory data was subsequently entered into stoichiometric equations to calculate fatty acid oxidation (FAO; g·min−1) and carbohydrate oxidation (CHO; g·min−1). Data was analysed using a paired samples t-test and a factorial repeated-measures analysis of variance (ANOVA) with Bonferroni post-hoc tests implemented and effects sizes (Cohen’s d) calculated. There was no significant difference reported for the time (min) to complete the exercise test (P > 0.05). No statistical differences were found between conditions for all other data (all P > 0.05) at any stage during the test with the main effects showing similar results (P > 0.05). Although no significant difference was shown, the current study provides an insight into the metabolic effects of CM during bouts of low-to-moderate intensity exercise. In addition, it contributes to the growing literature regarding CM and could be useful in the sports nutrition and weight loss industries.