Citrulline

Citrulline is a non-essential amino acid that is naturally produced by the body and can be found in high doses in some foods such as watermelon. Citrulline can either be supplemented in its amino acid form as L-citrulline or as citrulline malate, which contains a malic acid component thought to improve anaerobic energy production. The supplement dosing will vary depending on the form chosen. (Allerton 2018)

L-citrulline is often supplemented to increase exercise performance (both aerobic and anaerobic) and has also been shown to improve recovery. L-citrulline has several metabolic effects, demonstrating increased muscle protein synthesis in skeletal muscle, increased mitochondrial biogenesis, and improved lipolysis (Allerton 2018). The mechanisms for improving performance and recovery include increasing endurance, decreasing fatigue, and reducing muscle soreness following exercise. Citrulline also serves as a nitric oxide precursor meaning L-citrulline supplementation may increase nitric oxide availability leading to aerobic performance improvements (Jones 2016). 

A study examining high-intensity cycling found that short-term L-citrulline supplementation lead to longer endurance performance, faster oxygen uptake, and a 21% increase in blood nitrate sensitivity (Bailey 2015). This suggests that dietary supplementation of L-citrulline can be effective at improving exercise performance and aerobic metabolism in healthy individuals. 

Another study examining the effects of a single dose of citrulline malate on anaerobic bench press performance and muscle soreness following exercise found a >50% increase in repetitions performed in the last set along with a 40% decrease in muscle soreness 24 and 48 hours after the session (Pérez-Guisado 2010). 

Citrulline appears to improve exercise performance in both supplemental forms. L-citrulline supplementation can improve oxidative metabolism and enhance endurance exercise performance. Alternatively, supplementation with citrulline malate shows to be useful in increasing anaerobic exercise performance during high-intensity activity while also mitigating soreness post-exercise. Supplementing 3-6g/day of L-citrulline and 6-8g/day of citrulline malate is the recommendation for performance benefit. There does not appear to be any adverse effects of citrulline supplementation. (Bailey 2015, Pérez-Guisado 2010)

References

Allerton TD, Proctor DN, Stephens JM, Dugas TR, Spielmann G, Irving, BA (2018). l-citrulline supplementation: Impact on cardiometabolic health. Nutrients, 10(7), 921.

Bailey SJ, Blackwell JR, Lord T, Vanhatalo A, Winyard PG, Jones AM (2015). l-citrulline supplementation improves O2 uptake kinetics and high-intensity exercise performance in humans. Journal of Applied Physiology. 119(4), 385-395.

Jones AM (2016). Dietary Nitric Oxide Precursors and Exercise Performance. Gatorade Sports Science Institute. Retrieved March 01, 2019, from https://www.gssiweb.org/sports-science-exchange/article/sse-156-dietary-nitric-oxide-precursors-and-exercise-performance

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