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Definition: "An ergogenic aid is any substance or phenomenon that enhances performance "

30.05.2010

NO boosters taken before strength training lower growth hormone peak

If you take a dose of L-arginine – the most important active ingredient in most NO boosters – just before a strength training session, it reduces your growth hormone production during the training. Sports scientists at Syracuse University discovered this when they gave 7 g L-arginine [structural formula shown below] to 8 bodybuilders.

L-arginine is an interesting amino acid for strength athletes. Fat people who lose weight lose less muscle tissue but more fat tissue if they take an extra 8 g L-arginine daily. [Am J Physiol Endocrinol Metab. 2006 Nov;291(5):E906-12.] If you fatten rats, they gain more muscle tissue and less fat if you mix L-arginine with their food. The same happens to piglets during a growth spurt. [Amino Acids. 2009 May;37(1):169-75.]

L-Arginine turns into nitrogen monoxide (NO) in the body. NO plays a key role in muscle enlargement as a result of training. [J Appl Physiol. 2002 May;92(5):2005-11.] [Mol Biol Cell. 2000 May;11(5):1859-74.] On top that, androgen receptors need NO to function. [J Endocrinol. 2004 Nov;183(2):343-51.] For these reasons the supplements industry launched NO boosters on the market.

Not all sports scientists agree on the matter, but there's a popular theory which says that strength training is more effective if you produce more anabolic hormones like testosterone and growth hormone as a result. But according to the researchers at Syracuse University, you produce less growth hormone if you take L-arginine just before training.

The figure below is based on tests done on 8 bodybuilders aged between 18 and 25. On one occasion the test subjects were given 7 g L-arginine or a placebo on an empty stomach and then did no exercise. On the following occasion, half an hour after administration they trained the main muscle groups, doing lat pull-downs, leg-extensions, bench-press, leg-curls, military-press, leg-press, triceps-extensions, biceps-curls and back-extensions. The subjects did 3 sets of each exercise and trained at 80 percent of the weight at which they could just manage 1 rep. They rested for 90 seconds between sets.

If you do no exercise, L-arginine raises your GH production. If you do weight training, L-arginine flattens off your GH peak. The figure below shows the total amount of growth hormone that the subjects produced during the first three hours after taking the L-arginine.

According to the instructions on the label of most NO boosters you should spread your intake over the day, and not take them just before training: good advice. Then you'd avoid lowering your growth hormone peak, but still provide your muscle cells with more NO to help activate the hypertrophy process.

A recent study has shown that power lifters produce more GH if they take 10 g L-arginine, but spread out over the day.

Source:
J Appl Physiol. 2006 Sep; 101(3): 848-52.