Glycine Propionyl-L-Carnitine (GlycoCarn) or GPLC is a propionyl ester of carnitine that includes an additional glycine component. Propionyl-L-carnitine is an amino acid that is naturally produced in the body. According to rxlist.com : “Propionyl-L-carnitine helps the body produce energy. It is important for heart function, muscle movement, and many other body processes. It also seems to help increase circulation.”
Glycine Propionyl-L-Carnitine benefits for bodybuilders
Now that you know what is glycine propionyl-l-carnitine and what does it do we should get right to the point and tell you what science has to say about its supplementation as ergogenic aid. However, almost all scientific literature available on glycine propionyl-l-carnitine is funded by its manufacturer and patent holder Sigma-tau HealthScience.
While still being relatively new to the family of sport nutrition supplements, athletes are already reporting favorable results regarding exercise performance. However, one of the earlier studies  in sedentary subject didn’t yield any performance enhancing effects. The results of this study suggested that up to 3 grams per day of glycine propionyl-l-carnitine for 8 weeks in conjunction with aerobic-exercise training is ineffective for increasing muscle carnitine content and without significant effects on aerobic or anaerobic exercise performance.
On the other hand, a double-blind, placebo-controlled, cross-over study by Patrick L. Jacobs and colleagues  noted very favorable performance effects of Glycine propionyl-l-carnitine. Twenty-four resistance trained males consumed either 4,5 grams of Glycine propionyl-l-carnitine or a placebo on two different days separated by one week. Results indicated that power output was significantly higher (up to 15%) compared to placebo. Blood lactate was 15 – 16% lower post-exercise with GPLC.
A 2010 study by Bloomer and others  compared GlycoCarn® and three different (better selling) pre-workout nutritional supplements on exercise performance in men. Nineteen resistance trained men performed tests of muscular power in a randomized, double-blind, cross-over design. None of the products tested in this study yielded any statistically different results with regards to exercise performance. GlycoCarn® resulted in the highest skeletal muscle oxygen saturation, although not of statistical significance.
While many athletes now use Glycine propionyl-l-carnitine as dietary supplement, future work (especially independent) is needed to better assess its effectiveness.
Glycine Propionyl-L-Carnitine side effects and safety concerns
According to rxlist.com : “Propionyl-L-carnitine is safe for most people. It can cause nausea, vomiting, stomach pain, weakness, and chest pain (angina). It can also cause a “fishy” odor of the urine, breath, and sweat.”
- Propionyl-L-Carnitine – Retrieved from http://www.rxlist.com/propionyl-l-carnitine/supplements.htm at 20. April 2013
Smith, Webb A., et al. “Effect of glycine propionyl-L-carnitine on aerobic and anaerobic exercise performance.” International journal of sport nutrition and exercise metabolism 18.1 (2008): 19.
Jacobs, Patrick L., et al. “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 6 (2009): 9.
Bloomer, Richard J., et al. “Research article 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.” (2010).