[ Editor's Note: Industry experts and bodybuilders alike have been keeping a close watch on a remarkable development in the pre-workout supplement category . Arginine-based muscle pump complexes have long been the supplement of choice for athletes looking to enhance sports performance and nutrient delivery to muscle tissue. Recently, however, an innovative and entirely new technology has emerged on the scene, impressing athletes with its capacity for unleashing dramatic increases in muscle size support and vascularity. That technology, glycine propionyl-L-carnitine hydrochloride (or GPLC), is so new that its availability is limited to a handful of supplements on the market (BioQuest's new muscle enhancement catalyst Alpha Fury among them). We asked supplement science expert Dwayne N. Jackson, PhD, to evaluate the new science, give us updates on the clinical investigations into its efficacy, and provide a detailed analysis of this promising compound for our readers.]

Preworkout supplements have taken the industry by storm and manufacturers claim that using them will increase blood flow (via increased nitric oxide production), energy, strength, and endurance. Most of these products contain blends of similar science-backed ingredients, but very few have undergone rigorous testing to confirm their effectiveness in a cocktail; thus, we are left having to trust anecdotal evidence. One considerably new player on the preworkout supplement scene is GlycoCarn, a patented compound with the chemical name glycine propionyl-L-carnitine hydrochloride (GPLC). GlycoCarn is currently the only USP grade GPLC supplement on the market, with an abundance of research to attest its purity and effectiveness. As inferred by its name, it is a propionyl ester of carnitine with a glycine attached to it. Of note, in less than 5 years, scientific evidence has shown that this relatively simple compound increases plasma nitric oxide, enhances energy metabolism, and improves exercise performance.

Unlike studies conducted on many other "nitric oxide boosters", the research on GPLC has been conducted on healthy humans using randomized, double blinded, placebo controlled, crossover experimental trials. Earlier published research has shown that GPLC supplementation increases resting nitric oxide levels (as measured by plasma nitrate/nitrite); an effect that has been confirmed in resistance trained men. In a recent article published in the International Journal of Vitamin and Nutrition Research, researchers from the University of Memphis reported that after 8 weeks of daily GPLC supplementation combined with aerobic training, blood nitric oxide levels increased by 38%, where those who received a placebo had no change from baseline levels. The researchers also noted decreased lipid peroxidation (due to greater antioxidant capacity) in those who received GPLC during the training period, with no change noted in the placebo group.

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In 2009, scientists from Florida Atlantic University studied the effect of GPLC supplementation on anaerobic exercise performance and blood lactate levels. This randomized, placebo controlled, crossover study was conducted on 24 resistance trained males, who completed five sets of 10 sec all-out sprints separated by 1 minute rest periods. The exercise testing was performed 90 minutes after the subjects ingested either 4.5g of GPLC or a placebo. The researchers reported that peak and mean power across the five sprint bouts was 2.6 - 15% greater and post-exercise blood lactate was 16% lower with GPLC compared to placebo. These findings are very applicable to bodybuilders, as the exercise paradigm used in this study represents a similar intensity and work to rest duration used in bodybuilding resistance training programs.

In a recent report published in the Journal of the International Society of Sports Nutrition, scientists from the University of Memphis compared the effects of 4 pre-workout nitric oxide boosters (including GPLC) on skeletal muscle oxygen saturation, blood nitric oxide, lactate, malondialdehyde, and exercise performance. Making this study directly translatable to bodybuilders, 19 resistance trained men performed tests of muscular power (bench press throws) and endurance (10 sets of bench press to failure). The subjects were randomized to 1 of 4 supplement groups or the placebo group and were instructed to consume the assigned supplement prior to exercise testing. Remarkably, none of the products except for GPLC resulted in beneficial changes. It was reported that a single dose of GPLC promoted increased skeletal muscle oxygen saturation at the onset of exercise, decreased fat peroxidation (a result of high antioxidant activity), and increased total exercise volume load compared to all other groups.

Overall, the current research indicates that GPLC is a safe and very promising preworkout supplement with high antioxdant capacity that increases blood nitric oxide levels and decreases postexercise blood lactate. All in all, these effects may lead to faster recovery between sets and increased exercise performance. From the presented research, it seems that GPLC may be one of the few true nitric oxide boosting supplements available. However, due to the novelty of this compound, research is relatively limited; as such, it may take a few years for all of its benefits and biological mechanisms to be reported.

Bloomer RJ, Tschume LC, & Smith WA. Glycine Propionyl-L-Carnitine modulates lipid peroxidation and nitric oxide in human subjects. The International Journal of Vitamin and Nutrition Research, 79(3):131-41, 2009.

Bloomer RJ, Smith WA, & Fisher-Wellman KH. Glycine Propionyl-L-Carnitine increases plasma nitrate/nitrite in resistance trained men. Journal of the International Society of Sports Nutrition, 4: 22, Dec 3, 2007.

Jacobs PL, Goldstein ER, Blackburn W, Orem I, Hughes JJ. Glycine Propionyl-L-Carnitine produces enhanced anaerobic work capacity with reduced lactate accumulation in resistance trained males. Journal of the International Society of Sports Nutrition, Apr 2;6:9, 2009.

Bloomer RJ, Farney TM, Trepanowski JF, McCarthy CG, Canale RE, Schilling BK. Comparison of pre-workout nitric oxide stimulating dietary supplements on skeletal muscle oxygen saturation, blood nitrate/nitrite, lipid peroxidation, and upper body exercise performance in resistance trained men. Journal of the International Society of Sports Nutrition, 7:16, 2010.

Jacobs PL, Goldstein ER. Long-term Glycine Propionyl-L-Carnitine supplementation and paradoxical effects on repeated anaerobic sprint performance. Journal of the International Society of Sports Nutrition 2010 , 7;35