Metabolic Inertia in Contracting Skeletal Muscle: The Expanding Role of the Carnitine Pool

The ability of the muscular carnitine pool to accept and temporally donate acetyl groups (from and towards the coenzyme A pool) is an important functional role of carnitine within biological systems that is often overlooked within the scientific literature. The present review will discuss recent research demonstrating the existence of a period of inadequate acetyl-CoA delivery towards the tricarboxylic acid cycle (the so-called ‘acetyl group deficit’), which occurs as a consequence of the impaired integration of cytosolic (glycolysis) and mitochondrial energy producing pathways at the onset of muscular contraction; due to a lag in the activation of the pyruvate dehydrogenase complex. During this period of inadequate acetyl-CoA delivery, acetyl groups can be sequestered from the limited muscular acetylcarnitine reserve in an attempt to sustain continued tricarboxylic acid cycle flux. Following on from this, the present review will highlight the metabolic and functional benefits to be gained by overcoming this period of metabolic inertia, through elevating the concentration of acetylcarnitine prior to physical exercise; in the presence and absence of pyruvate dehydrogenase complex activation and through appropriately timed ‘warm-up’ exercise.