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Popular Bodybuilding Supplement Does Not Improve Muscle Strength

Renee DespresFriday, June 15, 2012 - 20:40

A popular bodybuilding supplement does not live up to its labels’ promises of improved muscle strength and endurance, said two unrelated groups of researchers this summer. The supplement, arginine-alpha-ketoglutarate (AAKG), is widely marketed as a strength-enhancer to weight lifters and bodybuilders. For example, AAKG is supposed to “extend muscle pump, enhance muscle growth, and get rock-hard muscles.” Evidence from these two studies, however, suggests that AAKG may actually decrease performance and have no effect on blood flow.

AAKG May Reduce Muscular Endurance

In July, a research team from Sacred Heart University in Fairfield, Connecticut, reported that AAKG supplementation may reduce muscular endurance, in contrast to claims that arginine supplements enhance muscular endurance. The researchers set out to determine whether AAKG taken shortly before an exercise bout affects local muscle endurance of the arm and shoulder girdle or the blood pressure (BP) response to anaerobic exercise. The reseach team reported their findings in the Journal of Strength and Conditioning Research.

The researchers recruited 12 men in their early twenties, all of whom regularly spent time lifting weights and engaging in other resistance training. performed two trials of exercise separated by at least 1 week. One group of men consumed a serving of a nutritional supplement containing 3,700 mg of AAKG both four hours before and 30 minutes before exercising. Half the men consumed a placebo. Before each exercise session, the men sat and rested for 16 minutes before researchers took their blood pressure. Blood pressure was measured again 5 and 10 minutes after the men completed the exercise session. The researchers repeated the procedure at least one week later.

During the exercise sesssion, the men performed three sets each of chin-ups, reverse chin-ups, and push-ups, each time lifting until they could not lift the weights one more time. The men were allowed three minutes of rest between each set of exercises.

When the researchers analyzed the data, they found that the AAKG supplementation did not improve muscle endurance or significantly affect the blood pressure response to anaerobic work. In fact, men in the study who took the supplements performed fewer total chin-ups and total trial repetitions. In addition, men in the supplement group could do fewer reverse chin-ups during the second set compared to men who received a placebo.

The researchers concluded that AAKG supplementation may hinder muscular endurance and suggested the use of these supplements before resistance training should be questioned.

AAKG Does Not Increase Blood Flow

Findings published in the August issue of the International Journal of Sport Nutrition and Exercise Metabolism also called into question claims about AAKG. According to dietary supplement manufacturers, AAKG increases nitric oxide production, which causes blood vessels to widen (called vasodilation) and steps up blood flow to the working muscles. In turn, the story goes, enhanced blood flow to working muscles during resistance exercise increases muscle strength more than exercise alone.

But a team of investigators from Baylor University found nothing to substantiate those claims when they measured blood flow after AAKG supplementation. The investigators were led by Dr. Darryn Willoughby, associate professor of exercise, nutritional biochemistry and molecular physiology at Baylor University.

Willoughby’s team asked 24 men to consume NO2 Platinum, a nutritional supplement containing AAKG, for 7 days. The investigators then had the men engage in a bout of weight lifting, or 'resistance exercise," and measured blood flow in arteries in the men’s arms. Blood flow was measured both before the men started taking the supplement and after seven days. After seven days of taking the AAKG-containing supplement, the men showed no significant difference in movement of blood.

Although the researchers did see a slight increase in blood flow, they attributed it to the exercise itself, not the supplement. Willoughby observed, “The data appear to refute the alleged supposition and manufacturer’s claims that ‘vasodilating supplements’ are effective at causing vasodilation, thereby resulting in increased blood flow to active skeletal muscle during resistance exercise. Furthermore, we specifically demonstrated that a single bout of resistance exercise increases vasodilation, arterial blood flow and circulating nitric oxide levels, but that the AAKG supplement provided no additive, preferential response compared to a placebo.”

Although both studies were small and limited in duration, they suggest what most exercise physiologists and kinesiologists – and athletes – already know: There’s no magic supplement that will suddenly make you superman or superwoman. A healthy, balanced diet combined a well-designed resistance training routine is the best way to build muscle strength and endurance.

References

Greer BK, Jones BT. Acute arginine supplementation fails to improve muscle endurance or affect blood pressure responses to resistance training. J Strength Cond Res. 2011 Jul;25(7):1789-94.

Willoughby DS, Boucher T, Reid J, Skelton G, Clark M. Effects of 7 days of arginine-alpha-ketoglutarate supplementation on blood flow, plasma L-arginine, nitric oxide metabolites, and asymmetric dimethyl arginine after resistance exercise. Int J Sport Nutr Exerc Metab. 2011 Aug;21(4):291-9.