The effect of regular physical exercise alone on metabolic control in NIDDM is quite variable and frequently of small magnitude. Greater improvement in glucose homeostasis can usually be obtained by weight loss.
Despite the relatively small impact of exercise demonstrated to date, regular physical exercise may be a therapeutic component supplementing diet in selected patients.
There is epidemiologic and clinical evidence that physical activity may reduce the incidence of coronary heart disease (CHD) in the general population. The risk-benefit ratio of exercise in NIDDM remains to be defined. Because many of the complications of NIDDM are related to atherosclerotic cardiovascular disease, an increase in physical activity for NIDDM patients appears prudent.
This recommendation is made despite the absence of conclusive studies and with recognition that improvements in CHD risk factors may not occur in those with NIDDM. Furthermore, the consensus panel seeks to emphasize that the possible benefits of body fat reduction outweigh putative exercise effects.
Vigorous exercise appears to blunt the rise in blood glucose that follows carbohydrate ingestion. In addition, exercise training may increase insulin sensitivity, but this change appears to be an acute effect associated with recent exercise and is reversed within 2 to 3 days by physical inactivity.
Physical activity may assist in reducing body fat, but exercise without caloric restriction appears ineffective. Patients who exercise regularly may negate its weight-reducing effects by curtailing their usual activities and by increasing caloric intake.
Complications of exercise in NIDDM patients include cardiac events (infarction, arrhythmias, and sudden death), bone and soft tissue injuries, and retinal damage in patients–particularly with proliferative retinopathy. The incidence of these complications with exercise has not been defined.
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NIDDM patients should undergo a thorough medical evaluation prior to increasing physical activity. The components of the evaluation will vary depending on the severity and duration of the diabetes, the presence of complications, the likelihood of asymptomatic CHD, and the intensity of the activity.
Because of the possible risks of retinal detachment and vitreous hemorrhage during exercise in patients with retinopathy, exercise that requires straining and breath holding (such as weight lifting) should be discouraged. Special attention should also be given to care of the feet during exercise.
In planning and recommending an exercise program for NIDDM patients, health professionals should be aware of several factors. The threshold of energy expenditure required to reduce postprandial hyperglycemia and to enhance insulin sensitivity has not been defined.
The same holds true for the use of physical activity in lowering the incidence of CHD. The panel believes that NIDDM patients should tailor an increase in their overall physical activity to their physical capacity, preferences, age, and lifestyle.
Also, because many of the metabolic effects of exercise are short-lived, it is extremely important that NIDDM patients choose exercises that they are likely to engage in frequently and continue over their lifetimes.