Health professionals know that exercise is a key component in the management of diabetes. Yet, how much is enough, and what type is best? These are frequent questions from patients who are trying to manage their blood sugar. Recommendations change frequently, adding to the confusion.
Randomized trials have shown clear benefits from lifestyle interventions on the progression of impaired glucose tolerance (IGT) to type 2 diabetes.1,2 The interventions in these studies included physical activity of ~2.5 hours per week and weight loss of as little as 5% to 7% of body weight. Other studies have placed patients in structured exercise programs with and without weight-loss interventions. Both groups had improvements in hemoglobin A1C, compared with the control group.3 Body weight was not significantly different in either group at the end of the study, indicating that the benefits demonstrated in this study were not related to weight loss.
The US Surgeon General's Report4 recommends 30 minutes of exercise daily?a regimen that many people may find difficult to incorporate into their daily schedule. Most clinical trials involving exercise interventions in diabetes have used a frequency of 3 times per week?a schedule that may be more manageable. The benefits of a day of exercise last from 24 to 72 hours, depending on the type of exercise.5 For this reason, the American Diabetes Association (ADA) suggests skipping exercise no more than 2 consecutive days.
Two types of exercise are recommended when developing a fitness program. Aerobic exercise helps improve cardiovascular health and insulin sensitivity. Resistance training improves insulin sensitivity to about the same extent as aerobic exercise, but it has the added benefits of increasing muscle mass, functional capacity, and resting metabolic rate.6 All of these parameters tend to decline with age, so resistance training is especially important in middleaged and older adults (with or without diabetes).
The ADA recently issued evidencebased guidelines designed to help people with IGT or type 2 diabetes to use exercise as an aid to controlling blood glucose.7 These recommendations include the following:
?A program of weight control that involves at least 150 minutes per week of moderate-to-vigorous exercise and a healthy diet with modest calorie restriction
?Physical activity consisting of 150 minutes or more of moderateintensity aerobic exercise (50%-70% of maximum heart rate) and/or 90 minutes of vigorous aerobic activity (>70% of maximum heart rate) per week. This activity should be done no less than 3 days per week, and no more than 2 consecutive days should pass without exercising. Patients can calculate their maximum heart rate by subtracting their age from 220.
?Exercising more than 4 hours per week to achieve greater cardiovascular risk reduction
?Exercising more than 7 hours per week to achieve long-term maintenance of major weight loss (>30 lb)
?Resistance training 3 times a week unless contraindicated. These exercises should target all major muscle groups. Supervision by a qualified exercise professional is recommended initially to make sure that the exercises are being performed correctly and to minimize the risk of injury.
Patients should consult their physician prior to starting an exercise program to rule out any contraindications to increased physical activity. Some conditions can increase the likelihood of cardiovascular problems or may be contraindications to certain types of exercise. Examples of these types of conditions include severe autonomic neuropathy, severe peripheral neuropathy, and preproliferative or proliferative retinopathy. The role of stress testing prior to beginning an exercise program is controversial, but such testing may be considered for patients who wish to undertake vigorous exercise and are at high risk for cardiovascular disease.
Some people with diabetes may experience hypoglycemia after exercising. For this reason, patients on insulin or secretagogues should check their blood glucose before, during, and after exercising. Alternate site testing is not recommended during exercise because of the possibility of rapidly changing blood glucose readings. Patients who are prone to episodes of hypoglycemia can eat extra carbohydrates. Some patients may require a reduction in their medication dose prior to exercise, but reducing it should be done only after consulting their health care professional.
Dr. Garrett is a clinical pharmacist practitioner at Cornerstone Health Care in High Point, NC.
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