Increasing muscle carnitine availability in humans and its impact on muscle fuel... - Prof. Stephens

Invited Session at ECSS MetropolisRuhr 2017 "Muscle Carnitine: The Key Player in Muscle Fuel Selection?"

Increasing muscle carnitine availability in humans and its impact on muscle fuel selection and regulation in exercise and health
Stephens, F.
University of Exeter

More than 95% of the body’s carnitine pool is confined to skeletal muscle, where it fulfils metabolic roles in the regulation of both fat
and carbohydrate oxidation, the major fuel sources utilised for mitochondrial ATP resynthesis during exercise. Firstly, as a substrate for carnitine palmitoyltransferase 1 (CPT1), carnitine facilitates the translocation of long-chain fatty acids across the otherwise impermeable mitochondrial membrane. Secondly, during high intensity exercise, carnitine buffers acetyl-CoA from excessive carbohydrate flux to acetylcarnitine, thereby maintaining a viable pool of free co-enzyme A (CoASH) to enable pyruvate
dehydrogenase complex (PDC) flux and mitochondrial ATP resynthesis to continue. It is, therefore, not surprising that carnitine
supplementation has been advocated as an ergogenic aid. This presentation will focus on studies that have increased skeletal
muscle carnitine content in humans to provide insight into the importance of these metabolic roles. In particular, studies
demonstrating that increasing skeletal muscle carnitine content by 15 to 20%, via 24 weeks of L-carnitine feeding in combination with
an insulinogenic beverage, can increase fat oxidation and energy expenditure during low intensity exercise, and result in a greater
acetylcarnitine accumulation and PDC activation during high intensity exercise. The implications of these metabolic effects for
exercise performance and health will also be discussed.