Exercise for diabetics: Effects of conditioning at constant body weight

Forty-eight physically inactive, overweight men (age 33 to 69 years) with non-insulin-dependent diabetes mellitus (NIDDM) or impaired glucose tolerance that did not require insulin or oral hypoglycemic agents underwent 12 weeks of exercise conditioning. Body weight was kept constant. Subjects were randomly assigned to one of five training programs, each of which offered different combinations of intensity, duration, and frequency. Subjects walked on a treadmill under supervision at either 50 % or 70% of their heart rate reserve for 30 or 60 minutes either two or four times per week. Mean estimated maximal oxygen uptake increased 5.5% for the 48 subjects. Although body weight was kept constant, training resulted in a significant reduction in skinfold thickness (P < .04). There was no associated significant improvement in diabetic control, glucose tolerance, plasma insulin, or glucagon levels in any group. Plasma lipid levels also did not significantly change with any training regimen. It is concluded that moderate exercise at the levels used in the present study is ineffective as sole therapy for NIDDM. This does not preclude the possibility that longer-duration, higher-intensity exercise might be more effective, but this remains to be proved. Precautions are advised in encouraging high-intensity, unsupervised exercise in middle-aged diabetics because of the possibility of latent coronary artery disease, as suggested in the present study by findings of ischemic electrocardiographic responses to exercise testing in a significant percentage of the men studied.