Citrulline has been touted as an ergogenic aid due to its promotion of vasodilation and blood flow by indirectly increasing nitric oxide synthesis. However, research on citrulline suggests that its effect on exercise performance is not as substantial as some claim.
For instance, 2 meta-analyses found that citrulline supplementation did not improve strength[1] or measures of aerobic exercise performance,[2] whereas other meta-analyses found that supplementation with citrulline reduced rating of perceived exertion (a subjective measure of the difficulty of an exercise), decreased muscle soreness, and increased power output and total repetitions performed in resistance training.[3][4][5]
It’s important to note that these mixed findings may be related to variations in study populations, doses, formulations, or lengths. Although certain studies found that supplemental citrulline does not improve some aspects of exercise performance, the totality of the evidence shows that it may be mildly helpful for some aspects of resistance training. Further research is needed to see whether changing these variables (e.g., higher doses) can improve exercise performance.