<body><h1>Glycine Propionyl-L-Carnitine</h1><p> </p><p> syn. GPLC</p><p> syn. Glycine-PLC </p><p> </p><p><div id=’imgblock’><img data-pointer=’9111’/></div></p><p> </p><h2> Description: </h2><p> Glycine propionyl-L-carnitine (GPLC) consists of propionyl-L-carnitine (PLC) bonded with the amino acid glycine. The body ultimately breaks these bonds, so that the active constituents are provided to cells in their free (utilizable) forms. PLC and glycine both may have vasodilatory properties, which can increase blood flow to peripheral tissues.411,412 This may aid endurance performance by helping to supply oxygen to the muscles, and also assist in the delivery of nutrients to muscles that are damaged/repairing. Studies suggest that the supplementation of GPLC can induce vasodilation by increasing nitric oxide levels. They also support some acute performance enhancing benefits in healthy trained adults, although further evidence is needed to confirm significant ergogenic value with regular use.</p><p> </p><p> <div id=’imgblock’><img data-pointer=’7467’/></p><p> Propionyl-L-carnitine is the propionate ester of carnitine, a cofactor in the metabolism and transport of fatty acids. Among other things, carnitine helps with the transport of certain long-chain fatty acids. It also enhances fatty acid oxidation, which may allow more ATP to be available for muscle cells. The propionic acid form of carnitine appears to have a higher affinity for muscle carnitine transferase, and thus may be more effective at increasing local tissue concentrations.413 Propionic acid is also a substrate for the formation of succinate, which is involved in the Krebs energy cycle. As such, its addition may help provide energy during hypoxic (low oxygen) conditions. PLC has been shown to increase exercise capacity in certain diseased states, such as peripheral arterial disease.414 Glycine is the smallest of the 20 common amino acids used in the manufacture of proteins. It is a non-essential amino acid, and is readily synthesized from serine when dietary intake is insufficient. Glycine is also an important neurotransmitter in the central nervous system, and is involved with the biosynthesis of many compounds including certain peptides, creatine, bile salts, glycogen, hemoglobin, ATP, and nucleic acids. Research suggests that glycine supplementation might possess some ergogenic value with regard to protein utilization, energy, metabolism, and endurance. Studies with exercising adults, however, have had conflicting and unclear results.415</p><p> </p><h2> Promoted Benefits:</h2><p> Glycine propionyl-L-carnitine is promoted to increase nitric oxide synthesis, peripheral blood flow, and cellular energy, as well as to improve fatty acid and carbohydrate metabolism, reduce muscle tissue damage (anti-catabolic), increase the removal of lactate, and improve overall sports/exercise performance. </p><p> </p><h2> Clinical Studies: </h2><p> This ingredient has been shown to improve performance in placebo-controlled studies with trained adults. Its Clinical Support Rating is 5 (5/5).</p><p> The most widely referenced placebo-controlled performance study published on glycine propionyl-Lcarnitine involved its supplementation by a group of experienced resistance-trained men.416 Each subject consumed a single dose of 4.5 g before being evaluated for exercise performance, which involved a series of five 10-second cycle ergometer sprints against resistance. Subjects taking GPLC noticed a 2.6-15% increase in peak and mean anaerobic power compared to placebo. There were also statistically significant and strong trends of reduced serum lactate (15.7- 16.2%) with GPLC supplementation. </p><p> </p><p> A second placebo-controlled study failed to find significant benefit to glycine propionyl-L-carnitine supplementation.417 It examined the effects of two dosage levels of GPLC (1 g and 3 g) on exercise performance in a group of healthy men and women. The subjects consumed the supplement for a period of eight weeks, during which time they also were subject to an aerobic exercise program. After eight weeks they were evaluated for muscle carnitine levels (vastus lateralis), VO2peak (peak oxygen consumption), exercise time to fatigue, anaerobic threshold, anaerobic power, and total work. Neither dose improved muscle carnitine levels or any marker of aerobic or anaerobic exercise performance compared to placebo. With regard to vasodilation, we find another relevant placebo-controlled study that examined the effects of continued glycine propionyl-L-carnitine intake by a group of healthy resistance-trained men.418 This investigation was focused on measuring serum nitrate (NOx) levels at rest and after exercise, which is a marker for nitric oxide production. The subjects consumed 4.5 g of GPLC per day for a period of four weeks. The exercise stimulus involved the use of an isometric handgrip dynamometer. The supplementation of glycine propionyl-L-carnitine tended to produce higher levels of NOx (and thus nitric oxide) after exercise compared to subjects taking placebo.</p><p> Although not all reports are in agreement, clinical studies do support the use of glycine propionyl-L-carnitine to improve acute exercise performance. Further research is needed to confirm if the regular use of GPLC can provide ergogenic value to trained adults.</p><h2> Empirical Evidence: </h2><p> Glycine propionyl-L-carnitine is widely available as a stand-alone nutritional supplement. The feedback on its use as a sport supplement tends to be positive. The main points of positive feedback usually involve its properties as a vasodilator (to increase the workout muscle “pump” effect), and ability to improve performance during prolonged (endurance-type) exercise. The feedback of GPLC with regard to muscle growth and resistance training results tends to be less consistently positive. A fair percentage of users fail to notice any benefit from GPLC use, even with regard to vasodilation. This appears to be consistent with a small percentage of “non-responders” noted in the nitrate studies discussed above. Whether this is due to an individual insensitivity to GPLC or other confounding variables remains unclear. Glycine propionyl-L-carnitine has an Empirical Evidence Rating of 4 (4/5).</p><p> </p><h2> Effective Dosage: </h2><p> Based on clinical studies, a dosage of 4.5 g per day is recommended. </p><p> </p><h2> Side Effects / Safety: </h2><p> Glycine propionyl-L-carnitine was well tolerated during clinical studies, with no significant side effects. Note that in higher doses, glycine sometimes causes gastrointestinal distress (nausea, vomiting, diarrhea) and a mild sedative effect.</p><p> </p><p> </p><p> </p></body>
