23 November 2011
L-arginine panned as performance booster
by George Atkinson
L-arginine, a popular supplement for athletes looking to boost performance, has been found to have a minimal effect on levels of nitric oxide, growth hormone, insulin, or insulin-like growth factor-1. The findings come from work done by physiologist Scott Forbes, from the University of Alberta.
L-arginine is popular as it is a precursor for nitric oxide that is known to improve blood flow, which in turn may aid the delivery of important nutrients to working muscles and assist with metabolic waste product removal. L-arginine has also been shown to increase growth hormone levels in the blood.
To see how these notions held up in the real-world, Forbes decided to test two different L-arginine doses on healthy, athletic men and record markers of nitric oxide, growth hormone, insulin, and insulin-like growth factor-1. "After a 10-hour overnight fast, and no breakfast, we gave them a different dose of L-arginine - either 0.075 g per kilogram of body mass for the low dose, 0.15 g per kg of body mass for the high dose, or a placebo," said Forbes.
Blood samples were then drawn with the athlete at rest, every half hour for three hours after the L-arginine or placebo dose. The reason explains Forbes, is that "Previous studies show that two hours after consumption L-arginine tends to reach baseline again."
Forbes found that in healthy, young, physically active males the two different doses significantly elevated L-arginine concentrations in the blood at rest, and both a low dose and a high dose were equally effective in doing so, but neither dose promoted a significant increase in nitric oxide, growth hormone, insulin, or insulin-like growth factor-1.
From these findings, it appears that L-arginine's impact depends on one's current health status: the more healthy and athletic the person, the less they'll benefit from it. Forbes has now embarked on two more studies - one with strength-trained athletes and one with aerobically-trained athletes - to look at the impacts of L-arginine on the body during exercise. "This time we're looking at the effects of supplements under two extremes: aerobic and strength exercise."
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Source: University of Alberta - Faculty of Physical Education and Recreation