Not that long ago, nitric oxide was known mainly as an air pollutant that came from car engines.

About 20 years ago, scientists discovered that it’s a critical signaling chemical in blood vessels that regulate blood flow. Healthy nitric oxide production is critical for any process in the body requiring blood flow.

Nitric oxide promotes wound healing following cuts, abrasions and injuries to muscles, tendons and ligaments. It also prevents atherosclerosis (hardening of the arteries), erectile dysfunction and diabetes.

So-called nitric oxide boosters marketed to fitness enthusiasts are supposed to increase muscle blood flow and promote muscle hypertrophy. L-arginine, used to produce nitric oxide synthase (an enzyme involved in making nitric oxide), is the most important ingredient in these supplements.

A review of literature by German scientists concluded that supplementing L-arginine improved the function of the endothelium – the cells lining the blood vessels that secrete nitric oxide. Scientists cite several studies showing improved blood vessel function in people with heart and blood vessel disease.

But the question that many people are asking is simply this: Do nitric oxide boosters help your weight training? The answer is too ironic – and it is “no” – which is also an abbreviation for “nitric oxide” (NO).

There aren’t any well-controlled studies that have shown that L-arginine or NO-boosting products increase muscle mass. [sources: European Journal of Clinical Pharmacology, The Journal of the American Medical Association, FitnessRX]