Amino Acid Supplement Free-Form Supports Exercise Recovery Energy and Detoxification L-Citrulline is a natural amino acid that supports sports performance and good health, while at the same time helping the liver detoxify. L-Citrulline helps the body rid itself of ammonia, a by-product of intense exercise. This clearing enables the body to recover after a workout, and it frees ATP energy for enhanced uses such as respiration and signal transduction.