The Type of Fuel Used in Muscular Exercise.

Abstract

In recent papers from the laboratory of A. V. Hill, the moot question of the type of fuel used in muscular exercise has again been raised. The evidence obtained led, in an earlier paper, 1 to the tentative conclusion that “muscular exercise, of such short duration that it does not seriously affect the general metabolism of the body, may be paid for primarily by the oxidation of carbohydrates.” In a later communication, Furusawa 2 states that whether the subject be on a carbohydrate or on a fat rich diet, short lived muscular exercise is performed only at the expense of carbohydrate. In more severe exercise, or in exercise of long duration, he postulates a conversion of fat to carbohydrate to replenish the depleted carbohydrate stores. The low respiratory quotients obtained during exercise on a high fat diet by Krogh and Lindhard 3 are, on this conception, due to the latter phenomenon, and would not, presumably, occur in mild exercise. The experiments of Anderson and Lusk, 4 who obtained R. Q.'s approaching those of fat in exercise during starvation, might conceivably, on this point of view, be explained on the ground that carbohydrate was no longer available.

We have recently determined the excess metabolism of exercise in 3 dogs, who were made to run on a horizontal treadmill. The total volume of CO₂ and O₂ exchanged was determined during a preliminary rest period, during the period of exercise, and during the period of recovery until the animal had returned to basal conditions (as shown by the gaseous exchange). The apparatus was accurate to within 2 per cent, as proved by repeated alcohol checks. The maximum deviations in the alcohol check R. Q.'s was from 0.654 to 0.677, the average being 0.664. In other words, the error of the R. Q. determinations in these experiments was hardly more than 0.01