THE METABOLIC EFFECTS OF STRENUOUS EXERCISE: A COMPARISON BETWEEN UNTRAINED SUBJECTS AND RACING CYCLISTS

Abstract

Previous investigations have suggested that post‐exercise ketosis is more marked in untrained subjects than in athletes. The present study was designed to exclude the possibility that the untrained subjects worked relatively harder. Four racing cyclists and five untrained subjects were studied during and after 20 min strenuous exercise on a bicycle ergometer. The work loads were adjusted so that the cyclists worked at least as hard, in terms of the heart rate attained, as the untrained subjects. Observations were made of respiratory gas exchange; blood samples were taken at rest, during and after the exercise and were analysed for ketone‐bodies and other metabolites, insulin and growth hormone.The racing cyclists worked at 1070 kpm/min with heart rate of 179·5 beats/min and oxygen consumption of 48 ml./min per kg body‐weight (means). The values for the untrained subjects were 715, 167 and 35 respectively. After exercise the concentration of ketone‐bodies in the blood increased progressively in both groups, reaching highest measured values 150 min after exercise. The increase was much smaller for all the racing cyclists. We conclude that post‐exercise ketosis is less in athletes even when they work as hard as or harder than untrained subjects.