The Influence of Previous Exercise upon the Metabolism, the Rectal Temperature, and the Body Composition of the Rat

Abstract

The oxygen consumption (at 30°C. and 24 hours after food) of four male rats was high immediately after exercise, and 1 hour after exercise it was still from 8 to 10 per cent above subsequent low periods. In from 2 to 4 hours after exercise the metabolism reached a plateau that was approximately basal for two of the rats but still from 6 to 8 per cent above basal for the other two rats. The average rectal temperature of nine male rats after exercise (39.0°) was 1.5° higher than the pre-work level (37.5°C.). During the first 40 minutes after exercise the temperatures fell rapidly and during the next 45 minutes remained essentially constant at a level, on the average, from 0.1° to 0.4°C. above the pre-work values. The average rectal temperature of non-exercised rats at noon was the same as in the morning, 37.4°C. Prolonged severe exercise (5486 meters daily) increased the basal heat production per square meter of body surface (measured 40 hours after exercise) only of growing male rats, but not of adult rats. Per unit of body weight, on the contrary, the metabolism of the exercised rats was much the same as that of their littermate controls, both during growth and during adult life. The picture is not clear because the controls were not of the same body weights as the exercised rats and were fed somewhat differently. Prolonged moderate exercise (1829 meters daily) did not modify the basal metabolism of the growing and adult male rats, either per unit of body weight or per unit of body surface. In this study the littermate controls were fed exactly the same as the exercised rats and weighed approximately the same. The basal metabolism of both groups of exercised rats and of the controls decreased with advancing age. The severely exercised rats (5486 meters daily for 120 days) consumed only about 24 per cent more food than the nonexercised rats. On the basis of fresh weight the bodies of the exercised rats contained 3.5 per cent less fat and 3 per cent more water than the bodies of the non-exercised rats. On the dry basis the exercised rats had an ash content 1.58 per cent higher, a nitrogen content 0.78 per cent higher, and a fat content 6.4 per cent lower, on the average, than the non-exercised rats. Variations in basal metabolism were not directly related to differences in ash, nitrogen, and fat content.