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

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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.

NO boosters taken before strength training lower growth hormone peak

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.

NO boosters taken before strength training lower growth hormone peak

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.

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