Fat metabolism in muscular exercise

Abstract

When normal healthy men performed muscular work on an ergometer bicycle at rates of 800-1200 kg. m. per minute, the blood-fat usually rose after about 8000 kg. m. of work had been done, the increase appearing earlier with greater rates of work. After recovery from a 1st period of work, a 2nd produced a rise more easily than usual. A high fasting blood-fat in normal or diabetic subjects led to a preliminary fall when work was performed; an abnormally low blood-fat was increased by relatively small amounts of work. This alteration was confined to the glyceride fraction, and the extra fat was probably derived from the adipose tissue. Continuance of work led to a return of the blood-fat towards normal (at about 18,000-21,000 kg. m.), and later to a 2nd rise. The CO2-combining power of the blood during muscular work of this type followed a course roughly the reciprocal of the blood-fat, but the changes preceded those in the blood-fat. The R. Q. for exercise and recovery was unity up to about 5000 kg. m., and thereafter fell steadily with increasing amounts of work. Analysis of the R. Q., O consumption, and N excretion showed that protein was not used for work, that carbohydrate continued to be used throughout though in decreasing amounts, and thatfat was used in increasing amounts. There was no relationship between fat utilisation and changes in the blood-fat concentration. No diminution in efficiency was observed at the lower R. Q., and the .figures did not suggest any conversion of fat to carbohydrate. Diabetic subjects, though performing work at a lower R. Q. than normals, showed no less efficiency, and no wastage of O. A modification of the Stewart and White (1925) method for the estimation of blood-fat is described.