Avid cyclists over the age of 50 had an improvement in their performance after taking arginine supplements for 3 weeks, according to a study published in the International Society of Sports Nutrition.

A group of 16 male cyclists, aged 50 to 73 years, were randomly assigned to receive either the supplement (Niteworks, from Herbalife International, Los Angeles, CA) containing 5.2 grams of L-arginine, or a look-alike placebo and instructed to continue with their usual cycling regimen over the 3-week study period.

After 3 weeks, those taking the supplement had an increase in their anaerobic threshold—the point at which lactate begins to accumulate in the blood, leading to fatigue.

“Arginine is involved in the production of nitric oxide in the body,” said Luigi Gratton, MD, vice president of medical affairs at Herbalife, “and nitric oxide has been associated with the improvement of exercise performance through its beneficial effects on the vascular system.” As people age, production of nitric oxide declines, so the researchers believed that arginine supplementation could support the production of nitric oxide and enhance performance.

The anaerobic threshold of the study subjects was assessed both before and after the 3-week study period. In those receiving the supplement, their anaerobic threshold increased by 16.7% after 1 week, and held steady during the 3 weeks, whereas those in the placebo group experienced no change.

“This indicates a potential role for arginine in improving exercise performance in older subjects,” said Dr. Gratton, “and improved performance could mean better fitness and healthier lives.”

The study, conducted at UCLA and funded by Herbalife, used Herbalife’s original formula Niteworks. The current product has a slightly different formula, although no changes were made to the active ingredients.