Glycine propionyl-L-carnitine: A Review of the Literature
"Not many people understand what a pump is; it must be experienced to be understood. It is the greatest feeling that I get. I search for this pump because it means that my muscles will grow when I get it. I get a pump when the blood is running into my muscles. They become really tight with blood. Like the skin is going to explode any minute. It's like someone putting air in my muscles. It blows up. It feels fantastic." —Arnold Schwarzenegger
The "muscle pump" in the past was strictly thought of as a temporary physiological condition in which the muscle was engorged with blood, which then leads to improved psychological well-being. However, many of the top physiologists thought that the pump had no role in the muscle growth process. But that view is now changing.
Nitric oxide synthase is an enzyme responsible for converting L-arginine into nitric oxide (NO). It is also the source of the highly sought-after pump. Today current research suggests that NO is more than just a vasodilator for good muscle pumps— it actually kickstarts the muscle hypertrophy process.
Previous studies reported that a spike in NO production triggers the release of hepatocyte growth factor (HGF) from its binding to the muscle extracellular matrix, leading to activation of satellite cells for muscle growth.1,2 This means that acute spikes in NO can enhance the anabolic response to exercise. The question now becomes: What supplements are the best for increasing nitric oxide?
L-arginine: Smoke and Mirrors
If you were to ask a bodybuilder a few years ago what the best nitric oxide supplement was, they probably would have said L-arginine. Unless you have been living under a rock or not reading MD, L-arginine is not worth crap for increasing vasodilatation in healthy young men. Young healthy weightlifters were administered 7 grams of L-arginine before resistance exercise and researchers examined several markers for vasodilatation or muscle blood flow.
Seven grams of L-arginine before resistance exercise did not have any effect on vasodilatation responses to resistance exercise in healthy young subjects. As expected, acute resistance exercise increased both the resting blood flow and the blood flow response to resistance exercise. Resting flow and peak exercise blood flow increased to a similar extent after both the placebo and L-arginine conditions in the study.
The study suggests that taking L-arginine alone before exercise has little effect on vasodilatation and its impact on nitric oxide.3 Another compound to be cautious about is Arginine alpha-ketoglutarate (AAKG), which is a salt of the amino acid arginine and alpha-ketoglutaric acid. At present, there is no research published in peer-reviewed journals to support the assertion that an increase in nitric oxide levels promotes greater muscle protein synthesis or improves muscle strength. There is also no evidence that the arginine alpha-ketoglutarate in "nitric oxide" supplements has any effect on nitric oxide levels in muscles.
Glycine propionyl-L-carnitine (GPLC): The Only Legit Nitric Oxide Stimulator
Antioxidants have been shown to enhance nitric oxide production by limiting oxidative stress, as oxidative stress decreases nitric oxide production. One of the reasons why smoking leads to high blood pressure is that it increases oxidative stress and blunts nitric oxide production.
One antioxidant nutrient that has received considerable attention is L-carnitine, with the amino acid precursor, glycine, also noted as having antioxidant properties. In fact, previous work involving animals has noted decreased oxidative stress following glycine use.5 The dietary ingredient glycine propionyl-L-carnitine (GPLC) has been shown to possess both antioxidant properties and to increase blood nitric oxide.4,6 This dual-action role makes this ingredient one to consider for both general health enthusiasts and athletes who are interested in improving antioxidant defense, while potentially stimulating an increase in blood flow due to the increased levels of nitric oxide.
Glycine propionyl-L-carnitine is marketed as GlycoCarn® by Sigma-tau HealthScience, Inc. This ingredient is USP-grade certified and consists of a molecular bonded form of propionyl- L-carnitine and one of the carnitine precursor amino acids, glycine.
GPLC Increases NO in Resistance-trained Men
Many studies involving supplements are done with rats or old men, which makes you say, "What the hell? I am a fricking hardcore gym junky; I want studies done on people like me!" So here are the studies that make it clear that GPLC is the clear choice for increasing NO. Unlike many studies, this research used resistance-trained men.
Study 1: In the first study, young resistance-trained men were subjected to a heavy resistance exercise protocol or a placebo. In the study, a total 4.5 g/d dosage of GPLC was administered before resistance exercise and measurements of NO were taken before and after exercise. They reported for the first time that oral GPLC can increase plasma NO in resistance-trained men.
The researchers noted a peak increase in NO from rest at 10 minutes post-exercise after taking GPLC. For example, the increase in NO from rest with GPLC was 16 percent and 17 percent at 3 and 10 minutes post-protocol, respectively. In addition, the specific mechanisms responsible for the increase in plasma NO with GPLC supplementation remain to be elucidated.6 Moreover, recent work indicates that PLC augments endothelial nitric oxide synthase (eNOS), the major enzyme responsible for NO production.
Study 2: The two high-intensity exercise trials were performed under two conditions, one with GPLC and one without. The study supplements (GPLC, PL) were provided by Jarrow Formulas (Los Angeles, CA) in 750 mg capsules, with six capsules equivalent to the 4.5-gram daily dose. The GPLC was the USP grade nutritional product, GlycoCarn.™ The assessment protocol consisted of five maximal effort 10-second cycle sprints performed with 1-minute active recovery periods between bouts. If you think about it, that's the typical duration of a set and most bodybuilders take short rest periods.
At the end of the study, GPLC had a 22.8 percent reduction in lactate accumulation per unit of power output.7 This means you can crank out more reps per set, which means a bigger and stronger muscle at the end of the day. The researchers speculated that the anaerobic benefits of GPLC are provided with high-intensity exercise via enhanced blood flow related to increased NO synthesis.
So hopefully I've now convinced you that GPLC is the only legit NO product. With that being said, you may go and pick up a NO product that contains GPLC, but more than likely you will be disappointed. In order to receive the full benefits of the pumps from GPLC, you must take the full dose! To match the dosages used with GPLC in research studies, you must take at least 4.5 grams per day. If you are taking less than that, you are going to be sadly disappointed. Find a product that contains the full dosage of GPLC and you will notice an improvement in not just your pumps, but also your work capacity.
References:
1. Anderson JE. A role for nitric oxide in muscle repair: Nitric oxidemediated activation of muscle satellite cells. Mol Biol Cell 2000, 11:1859-1874.
2. Anderson JE, Wozniak AC. Satellite cell activation on fibers: modeling events in vivo— an invited review. Can J Physiol Pharmacol, 2004; 82:300-310.
3. Fahs CA, Heffernan KS, Fernhall B. Hemodynamic and Vascular Response to Resistance Exercise with l-Arginine. Med Sci Sports Exerc, 2009 Mar 7.
4. Bloomer RJ, Tschume LC, Smith WA: Glycine propionyl-L-carnitine modulates lipid peroxidation and nitric oxide in human subjects. Int J Vitam Nutr Res.
5. Malyshev VV, Oshchepkova OM, Seminokii IZH, Nefedova TV, Morozona TP. The limitation of lipid hyeroxidation nad the prevention of stressor damages to the heart by glycine derivatives. J Exp Clin Pharmocol, 59, 23-25, 1996.
6. Bloomer RJ, Smith WA, Fisher-Wellman KH. Glycine propionyl-L-carnitine increases plasma nitrate/nitrite in resistance-trained men. J Inter Soc Sports Nut, 4: 22, Epub Dec 3, 2007.
7. Smith WA, Fry AC, Tschume LC, Bloomer RJ: Effect of glycine propionyl-L-carnitine on aerobic and anaerobic performance. Int J Sport Nutr Exerc Metab, 2008, 18:19-36.
Dus ja, dan schiet zo'n sample helemaal niet op 
, dat maakt het natuurlijk nog wat moeilijker.
ik push, maar mijn press komt pas een halve minuut later 
