Role of lipids on endurance capacity in man

A man whose weight is near 70 kg has approximately 15 kg of fat as triglycerides in adipose tissue, representing about 140,000 kcal. With such a quantity of stored fat, the question is to know why triglycerides are not the only fuel for exercise. Probably because this fuel cannot sustain maximal rates of exercise. The ability to sustain maximal exercise is dependent on carbohydrate use. The reason for the limited rate at which energy can be derived from fat store is not clear. We can examine successively: 1) The rate of release from adipose tissue. Hydrolysis of the adipose tissue triglyceride is regulated by hormonal and nervous influence. It has recently been shown that 70% of fatty acids released from adipose tissue at rest are reesterified. This value decreases to 25% at the onset of submaximal exercise at 40% of VO2max. One part of the increase in fat oxidation could therefore result from the reduced reesterification. 2) The capacity of transport and muscle extraction. A close correlation has been shown between the increase in FFA concentration and FFA uptake during increased energy expenditure under the effect of exercise. Exercise increases lipoprotein lipase (LPL) activity in muscle. This causes increase in muscle and cardiac FFA uptake and a decrease in LPL activity in adipose tissue. The control of this enzyme is coordinated by hormonal mechanisms resulting from the reduction of insulin and the increase in catecholamines induced by exercise.(ABSTRACT TRUNCATED AT 250 WORDS)