Daily variations of plasma glucose and insulin in physically-trained and sedentary subjects.

The variations in plasma glucose and insulin levels were measured at 30-minute intervals throughout the day in physically trained and in sedentary subjects. The subjects exercised for 75 minutes at 65% of VO2max in the first experiment and refrained from heavy exercise in the second experiment. In all situations the physically trained subjects overall had lower plasma glucose and insulin levels than the nontrained subjects. In addition, the positive correlation between plasma glucose and plasma insulin levels observed in the physically trained subjects was significantly smaller than that note in the nontrained subjects, indicating reduced insulin requirements in physically-trained persons. During the period of exercise, glucose levels increased significantly in the trained subjects only. In the period that followed exercise, that is between 1:30 PM and 9:00 PM, the physically trained subjects had plasma glucose levels that were higher than those noted during the comparable hours not preceded by exercise; no comparable difference were found with insulin. Calculation of the total area for insulin indicated a reduction of insulin requirement of about 40% associated with physical training.