Intramyocellular triacylglycerol as a substrate source during exercise

The role of intramyocellular triacylglycerol (IMTG) as a substrate source during exercise has recently regained much attention as a result of the proposed functional relationship between IMTG accumulation and the development of insulin resistance. It has been speculated that elevated NEFA delivery and/or impaired fatty acid (FA) oxidation result in intramyocellular accumulation of triacylglycerol and FA metabolites, which are likely to induce defects in the insulin signalling cascade, causing insulin resistance. The progressive accumulation of IMTG in sedentary patients and patients who are obese and/or have type 2 diabetes should therefore form a major therapeutic target, and efforts should be made to develop interventions that prevent excess IMTG accretion by stimulating their rate of oxidation. Although regular exercise is likely to represent such an effective means, there is much controversy about the actual contribution of the IMTG pool as a substrate source during exercise. The apparent discrepancy in the published literature might be explained by differences in the applied research protocol and the selected subject population, but most of all by the techniques that have been employed to estimate IMTG use during exercise. Data obtained in trained-endurance athletes indicate that athletes can substantially reduce their IMTG pool following a single exercise session. With the growing awareness that skeletal muscle has a tremendous potential to oxidise IMTG during prolonged moderate-intensity exercise, more research is warranted to develop combined exercise, nutritional and/or pharmacological interventions that can stimulate IMTG oxidation in sedentary patients and patients who are obese and/or have type 2 diabetes.