Oral L-Carnitine Supplementation and Exercise Performance

Abstract

Carnitine is an endogenous compound essential for energy production, playing dual roles as a component of fatty acid translocation through the mitochondrial membrane and as a buffer for accumulating acetyl CoA. In addition, it has been shown to improve muscle recovery and up-regulate androgen receptors, and has various effects on the brain. In the absence of either primary or secondary deficiencies, it is rare for healthy individuals to become deficient in carnitine. Studies have found that chronic training causes decreases in muscle carnitine concentration below baseline; thus, supplementation is recommended to at least stabilize carnitine levels. In this project, we review clinical studies that assess the effect carnitine has on exercise performance and metabolism in aerobic, anaerobic, and resistance training. Although findings have been inconsistent, research has demonstrated carnitine’s ability to improve exercise performance by increasing fatty acid oxidation, sparing glycogen, reducing lactate accumulation, increasing efficiency of glycogen utilization, decreasing rate of perceived exertion, and allowing a higher work output. We conclude that chronic ingestion of ~30 mg/kg/d of L-carnitine taken with carbohydrates can effectively increase muscle total carnitine concentration, enabling its ergogenic effects. More studies are necessary to determine optimal dosing of L-carnitine, the optimal dose of carbohydrates with L-carnitine, and the effect of L-carnitine on chronic training. No prior study has investigated the effect of chronic L-carnitine supplementation on chronic resistance training. We propose a 24-week parallel design, randomized, double-blind, placebo-controlled study. Participants will be healthy, resistance-trained men, observed to determine whether carnitine can be used to improve recovery, muscular endurance, and strength.