Citrulline is an amino acid and in the body, citrulline is converted by the kidneys and helps to increase levels of both arginine and ornithine. It has been shown to be more effective at increasing blood arginine levels than arginine supplementation and is, therefore, a better way of increasing nitric oxide production.
By increasing blood arginine levels citrulline causes the release of nitric oxide. Nitric oxide is responsible for vasodilation (expanding of the blood vessels) which increases nutrient delivery and the feeling of ‘muscular pump’. With improved nutrient and oxygen delivery to the working muscle, we see reduced fatigue and increased energy levels. Improved blood flow also means that harmful by-products of training such as lactic acid are removed more efficiently.
Furthermore, citrulline's ability to increase ornithine level means that other harmful toxins such as ammonia are removed from the body more efficiently. This helps to reduce fatigue further. These effects have been noted in studies on both aerobic and anaerobic activity, making citrulline a great choice regardless of whether you are a strength or endurance athlete.