It is thought to improve blood flow to exercising muscles. Increasing the delivery of nutrients, hormones, and oxygen to aid in recovery.
Arginine also boosts can boost growth hormone (GH) levels when taken on an empty stomach at bedtime. It is often combined with ornithine for that purpose.
Arginine has come under pressure recently as a NO booster and is being replaced in most pre-workouts with the arginine precursor citrulline.
The typical NO boosting dosage is 3-5g of arginine three times per day. Besure to take one dose 30-40 minutes before exercise.
Arginine HCL and Arginine-AKG seem to be the preferred forms although l-arginine is also often used.
People who are prone to getting cold sores are have a herpes condition should avoid arginine.
There are those who are saying that the oral application of arginine does not reap the benefits that intravenous applications have produced.
To see other uses for arginine, check out the wikipedia page.