L-arginine is the rate-limiting amino acid required for NO synthesis. Studies have shown that when large doses of L-arginine are ingested or infused directly into a blood vessel, there is a positive effect on increasing vascular function. Building on this information, researchers from the United Kingdom hypothesized that L-arginine supplementation would improve exercise efficiency and enhance performance.
Healthy men performed an exercise test on a cycle on two occasions. During one trial, they consumed 6g of L-arginine. During the second trial, they consumed a placebo.
One hour after taking the L-arginine and the placebo, subjects performed an incremental exercise test to exhaustion. The primary finding was that L-arginine supplementation reduced the amount of oxygen required to perform exercise. This means that individuals accomplished the same exercise load, but with less energy expended. In other words they were more efficient after supplementing with L-arginine. L-arginine supplementation also increased time to exhaustion by 26% during high intensity cycling.
These findings provide evidence that L-arginine supplementation (6g in a single dose) improves exercise efficiency and tolerance.