Arginine and vasodilation
For example, arginine is the rate-limiting amino acid in the synthesis of nitric oxide (NO), a gaseous substance that causes blood vessels to dilate. It’s well known that increasing the bioavailability of NO improves vasodilation and blood pressure, but emerging evidence suggests exercise efficiency and performance may benefit as well.
In one study, healthy men performed two separate exercise cycle tests one hour after consuming either 6 grams of arginine or a placebo. Arginine supplementation reduced the amount of oxygen required to perform exercise (i.e. increased exercise efficiency). This means that individuals accomplished the same exercise load but with less energy expended. Arginine supplementation also increased time to exhaustion by 26% during high intensity cycling.
Arginine and growth hormone
Other work has shown that arginine supplementation may increase growth hormone (GH). When arginine is infused directly into a vein, GH levels increase dramatically. In fact, arginine infusion is used clinically as a diagnostic test when GH deficiency is suspected. The dose of oral arginine needed to increase GH levels appears to be at least 5 grams, with larger responses shown with 9 grams.
Arginine and muscle gains
In a different study, a combination formula consisting of 7 grams of arginine, 1.5 grams of HMB, 7 grams of glutamine and 3 grams of taurine resulted in striking improvements in body composition. Compared to a control group who received a placebo, healthy young men who took these supplements during 12 weeks of heavy resistance training showed a 10-pound greater increase in lean body mass.