The Physiological Effects of Amino Acids Arginine and Citrulline: Is There a Basis for Development of a Beverage to Promote Endurance Performance? A Narrative Review of Orally Administered Supplements

Abstract

Nutritional and ergogenic aid supplementation is prevalent within athletic or general fitness populations, and is only continuing to gain momentum. Taken in isolation or as a combination, amino acid (AA) supplementation has the potential to increase endurance performance among other benefits. L-Arginine (L-Arg) and L-Citrulline (L-Cit) are two AAs proposed to increase endothelial nitric oxide (NO) synthesis, with potential additional physiological benefits, and therefore may contribute to enhanced performance outcomes such as increased power output, or time to exhaustion. However, the appropriate dose for promoting physiological and performance benefits of these AAs, and their potential synergistic effects remains to be determined. Therefore, the aim of this review was to evaluate the varied concentrations used in the current literature, assess the effects of L-Arg and L-Cit in combination on physiological responses and endurance performance, and consider if there is a fundamental basis for providing these supplements in the form of a beverage. A total of six studies were considered eligible for the review which utilized a range of 3–8 g of the AA constituents. The findings support the notion that supplementing with a combination of L-Arg and L-Cit may increase NO production, enhance vasodilation, and therefore increase performance capacity in athletes. A beverage as a carrier for the two AAs is worth considering; however, there remains limited research assessing these outcomes across a consistent range of concentrations in order to see their full potential.