Body weight and fat proportion were always lowest in exercising animals ( run daily on a motor driven treadmill since the 18th day of life for 2-3 hr per day, with a speed up to 18 m/min,-i.e., medium or mild exercise of an aerobic character) with the highest caloric intake. Highest weight and fat together with the lowest caloric intake were found in hypokinetic animals (housed in spaces 8 x 12 x 20 cm since weaning). These differences were most apparent after the end of exponential growth, i.e., approximately at 100-120 days of age. Additional exercise can manifest its impact in adult life relatively more markedly when the level of spontaneous physical activity is already declining.

Moreover, a higher level of metabolic activity was found in the adipose tissue in exercised animals; experiments with injected palmitate showed a lower inflow rate of fatty acids into the adipose tissue of the exercised animals, even when measured 24 hr after the last work load on the trdadmill. On the other hand, the inflow rate of palmitate into the heart and soleus muscle under the same conditions was significantly higher in the exercised animals, indicating a higher utilization of lipid metabolites after adaptation to aerobic exercise.

This was also proved by a higher level of lipoprotein lipase activity in the soleus and heart muscles, as well as an increased proportion of O2 in the expired air during the infusion of palmitate into the femoral vein during pentobarbital anesthesia. Hypokinesia mostly caused changes of an opposite character. The characteristically modified proportion of fat deposits resulted from a number of complex metabolic changes in the organism induced by long-term adaptation to a changed physical activity regimen-i.e., both by increased caloric intake and output in the exercised animals, or their reduced levels in the hypokinetic animals.

Some of the mentioned contrast are similar to differences between young and old animals. An appropriate level of physical activity seems therefore to play an important role in the fat metabolism and in the regulation of body composition. As follows from the above mentioned experiments, lack of physical activity can not be compensated for by a reduced caloric intake.

Mentioned changes in body composition, caloric intake, and lipid metabolism were manifested after adaptation to sufficiently intensive dynamic exercise of an aerobic character. When following these changes after static exercise, no significant changes were found