Muscular exercise in type I-diabetics. II. Hormonal and metabolic responses to moderate exercise

Abstract

In Type I-diabetics metabolic response to exercise is largely determined by the availability of exogenous insulin. The aim of the present study was to assess the metabolic response to moderate exercise of 24 insulin-dependent (Type I-) diabetics treated by multiple subcutaneous injections of short acting insulin. Differences in insulin availability (hypo- [trial A] or hyperinsulinemia [trial B]) resulted from the different periods of time that had elapsed since the previous insulin injection, i.e., after 3 hours (trial A), and 1 hour (trial B). Bicycle ergometer tests at intensities up to 75% VO2max, were carried out with patients and controls. Plasma glucose, FFA, glycerol, alanine, growth hormone and glucagon levels were measured during a period of 85 min. In both trials, physical exertion did not have a significant statistical effect on the glucose concentration in the blood of hypo- and hyperinsulinemics. Surprisingly, despite the different insulin availabilities FFA, glycerol, alanine and glucagon concentrations were not statistically different in either trial and appear similar to those of healthy controls. A normal metabolic response to exercise can thus also be expected in Type I-diabetics, provided adequate insulin is available. When compared to controls, growth hormone concentrations were found to have increased during exercise. These experimental data strongly suggest the great necessity of adequate insulin availability in order to obtain normal metabolic responses to exercise in insulin-dependent diabetics. Despite certain degrees of hypo- or hyperinsulinemia, moderate exercise did not cause any marked metabolic derangements. This type of moderate exercise is therefore recommended for improving metabolic control in such patients.