Abstract

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 liprotein 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. Thus, enhanced lipid availability resulting from eating a fatty meal before exercise, or a chronic high fat diet, or fasting, is not capable of enhancing endurance capacity in humans. The glucose-fatty acid cycle which has previously been proposed to spare muscle glycogen stores is not operative in man. Verf.-Referat