Metabolic Regulation of Fat Use during Exercise and in Recovery

Fat is an important fuel for exercise but plays a secondary role to carbohydrate (CHO). Increasing fat use during exercise can decrease the reliance on CHO and spare CHO for later in training sessions or competitions that depend on CHO for success. The pathways that metabolize and oxidize fat are activated more slowly than CHO at the onset of exercise and reach a maximum at moderate exercise intensities. As exercise intensity increases to similar to 75% VO2max and beyond, fat metabolism is inhibited: using CHO will increase the amount of energy produced per liter of oxygen consumed. The capacity for fat use during exercise is increased by aerobic training and the dietary combination of little or no CHO intake and high fat intake. Fat oxidation is very dependent on the mitochondrial volume of muscle but other key sites of regulation include release of fat from storage forms and fat transport across plasma and mitochondria! membranes. This chapter examines the control of fat metabolism during moderate and intense exercise with an emphasis on human findings and the adaptations that occur with aerobic training and other acute nutritional manipulations. Recent work using molecular and cellular compartmentalization techniques have advanced the knowledge in this area. Copyright (C) 2011 Nestec Ltd., Vevey/S. Karger AG, Basel