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Release Date: June 6, 2006; Valid for credit through June 6, 2007

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June 6, 2006 — The American Diabetes Association (ADA) developed a consensus statement with recommendations regarding exercise for patients with type 2 diabetes, and published it in the June issue of Diabetes Care.

"For decades, exercise has been considered a cornerstone of diabetes management, along with diet and medication," write Ronald J. Sigal, MD, MPH, from the University of Ottawa in Ontario, Canada, and colleagues. "However, high-quality evidence on the importance of exercise and fitness in diabetes was lacking until recent years. The present document summarizes the most clinically relevant recent advances related to people with type 2 diabetes and the recommendations that follow from these."

The authors also recently published a technical review on physical activity and exercise in type 2 diabetes that includes greater detail on individual studies, on prevention of diabetes, and on the physiology of exercise. They are also planning a subsequent technical review and ADA Statement on exercise in type 1 diabetes.

Recommended lifestyle measures for prevention of type 2 diabetes are as follows:

• People with impaired glucose tolerance should begin and continue a program of weight control, including at least 150 minutes per week of moderate to vigorous physical activity and a healthful diet with modest energy restriction (Level of evidence: A).
  
  
• The amount and intensity of recommended aerobic exercise vary according to goals. To improve glycemic control, assist with weight maintenance, and reduce risk for cardiovascular disease (CVD), the panel recommends 150 minutes per week or more of moderate-intensity aerobic physical activity (40% - 60% of oxygen consumption per unit time [VO_2max] or 50% - 70% of maximum heart rate), and/or 90 minutes per week or more of vigorous aerobic exercise (> 60% of VO_2max or > 70% of maximum heart rate). The physical activity should be distributed over at least 3 days per week, with no more than 2 consecutive days without physical activity (Level of evidence: A).
  
  
• Compared with lower volumes of activity, performing at least 4 hours per week of moderate to vigorous aerobic and/or resistance exercise physical activity is associated with greater CVD risk reduction (Level of evidence: B).
  
  
• For long-term maintenance of major weight loss (≥ 13.6 kg or 30 lb), larger volumes of exercise (7 hours per week of moderate or vigorous aerobic physical activity) may be helpful (Level of evidence: B).
  
  
• Unless contraindicated, people with type 2 diabetes should be encouraged to perform resistance exercise 3 times per week, targeting all major muscle groups. This should progress to 3 sets of 8 to 10 repetitions at a weight that cannot be lifted more than 8 to 10 times (level of evidence: A). Initial supervision and periodic reassessments by a qualified exercise specialist are recommended to ensure that resistance exercises are performed correctly, to maximize health benefits, and to minimize the risk of injury.

"Because of the increased evidence for health benefits from resistance training during the past 10 - 15 years, the American College of Sports Medicine (ACSM) now recommends that resistance training be included in fitness programs for healthy young and middle-aged adults, older adults, and adults with type 2 diabetes," the authors write. "With increased age, there is a tendency for progressive declines in muscle mass, leading to 'sarcopenia,' decreased functional capacity, decreased resting metabolic rate, increased adiposity, and increased insulin resistance, and resistance training can have a major positive impact on each of these. Resistance exercise improves insulin sensitivity to about the same extent as aerobic exercise."

The authors caution that before beginning a program of physical activity more vigorous than brisk walking, people with diabetes should be evaluated for conditions that might be associated with increased likelihood of CVD or that might contraindicate certain types of exercise or predispose to injury. Examples of such conditions could include severe autonomic neuropathy, severe peripheral neuropathy, and preproliferative or proliferative retinopathy. The patient's age and previous physical activity level should also be considered.

"The role of stress testing before beginning an exercise program is controversial," the authors write. "There is no evidence that such testing is routinely necessary for those planning moderate-intensity activity such as walking, but it should be considered for previously sedentary individuals at moderate to high risk of CVD who want to undertake vigorous aerobic exercise exceeding the demands of everyday living."

To prevent hypoglycemia, patients who take insulin or secretagogues should check capillary blood glucose before, after, and several hours after completing a session of physical activity, at least until their usual glycemic responses to such activity can be predicted. For those prone to hypoglycemia during or after exercise, useful strategies may include reducing doses of insulin or secretagogues before sessions of physical activity, consuming extra carbohydrate before or during physical activity, or both (Level of evidence: E; consensus, clinical experience).

"The most successful programs for long-term weight control have involved combinations of diet, exercise, and behavior modification," the authors conclude. "Exercise alone, without concomitant dietary caloric restriction and behavior modification, tends to produce only modest weight loss of [approximately] 2 kg. Weight loss is typically this small primarily because obese people often have difficulty performing sufficient exercise to create a large energy deficit, and it is relatively easy to counterbalance increased energy expenditure through exercise by eating more or becoming less active outside of exercise sessions."

Diabetes Care. 2006;29:1433-1438

Learning Objectives for This Educational Activity

• Describe specific guidelines for exercise to improve outcomes in patients with type 2 diabetes.
• Identify potential mechanisms for the benefits of exercise in patients with type 2 diabetes.

Clinical Context

Exercise together with diet and medications have been considered a cornerstone of diabetes management, but high-quality evidence for demonstrating its benefits was lacking until recently. Potential mechanisms by which exercise improves cardiovascular fitness in nondiabetic and diabetic individuals include decreased inflammation, improved early diastolic filling, improved endothelial function, and reduced abdominal fat.

The current consensus statement from the ADA summarizes the most recent evidence based on clinical trials and provides guidelines specific to patients with type 2 diabetes. The guidelines include recommendations for aerobic, resistance and flexibility exercises, duration and intensity recommended for glycemic control and cardiovascular protection, and contraindications to exercise in type 2 diabetes as well as the role of exercise in prevention of diabetes.

Study Highlights

• Higher levels of habitual aerobic exercise in the general population have been associated with lower cardiovascular and overall mortality.
• The US Surgeon General recommends 150 minutes per week of moderate intensity exercise for cardiovascular protection.
• There is no evidence that stress testing prior to an exercise program is necessary for diabetic patients, but testing is recommended for sedentary individuals at moderate to high cardiovascular risk.
• The US Preventive Services Task Force recommends that stress testing be avoided in individuals with low cardiovascular risk (less than 10% for 10 years).
• Approximately 150 minutes per week of exercise and diet-induced weight loss has been demonstrated to reduce the risk of progression from impaired glucose tolerance to type 2 diabetes by 58%.
• Diet alone, exercise alone, and diet and exercise combined are equally effective in slowing progression.
• In patients with type 2 diabetes, structured aerobic exercise for 8 weeks has been shown to reduce glycated hemoglobin (HbA_1c) levels from 8.3% to 7.6% (P < .001).
• The effect of aerobic exercise on HbA_1c level is independent of weight loss and not considered to be mediated by weight loss.
• Exercise alone produces modest weight loss of approximately 2 kg, but high volume aerobic exercise of 700 kcal daily is associated with greater fat loss and improved insulin sensitivity.
• Higher volume exercise (7 hours per week of moderate or vigorous aerobic exercise) is recommended to maintain major weight loss of 13.6 kg or more.
• To improve glycemic control, this guideline recommends at least 150 minutes per week of moderate physical activity.
• For cardiovascular protection, hours or more per week of moderate to vigorous aerobic and/or resistance activity are recommended in patients with diabetes.
• Exercise intensity predicts degree of lowering of HbA_1c level, and patients should be encouraged to increase exercise intensity to obtain additional benefits.
• The ACSM recommends resistance training for adults with type 2 diabetes.
• No serious adverse effects have been described in patients with diabetes who participate in resistance training.
• This guideline recommends resistance exercises at least 3 times per week targeting all major muscle groups progressing to 3 sets of 8 to 10 repetitions at a weight that cannot be lifted more than 8 to 10 times.
• The effect of a single bout of exercise on insulin sensitivity in patients with diabetes lasts 24 to 72 hours, whereas resistance exercise training may have a longer effect.
• 2 systematic reviews found that flexibility exercises did not reduce risk for exercise-induced injury.
• Physical activity should be avoided if fasting glucose levels are higher than 250 mg/dL, and ketosis is present.
• However, if the patient feels well, is well hydrated, and urine or serum ketone tests yield negative results, it is not necessary to postpone exercise based on hyperglycemia alone.
• Medication adjustments may be needed to prevent hypoglycemia in patients with diabetes who exercise.
• Recommendations for exercise in the presence of long-term complications are based mainly on expert opinion.
• Physical activity has not been shown to adversely affect progression of nonproliferative diabetic retinopathy and macular edema.
• Vigorous exercise should be avoided in the presence of proliferative or severe nonproliferative retinopathy because of the potential risk of vitreous hemorrhage or retinal detachment.
• Exercise is not contraindicated with diabetic renal disease.

Pearls for Practice

• Exercise in patients with diabetes has a protective effect on cardiovascular disease and improves glycemic control.
• The benefits of exercise in glycemic control are independent of weight loss. Mechanisms of cardiovascular protection include decreased inflammation, improved early diastolic filling, improved endothelial function, and reduced abdominal fat.

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News Author

Laurie Barclay, MD
is a freelance writer for Medscape.

Disclosure: Laurie Barclay, MD, has disclosed no relevant financial relationships.

Clinical Reviewer

Gary Vogin, MD
Senior Medical Editor, Medscape

Disclosure: Gary Vogin, MD, has disclosed no relevant financial relationships.

CME Author

Desiree Lie, MD, MSEd
Clinical Professor of Family Medicine; Director, Division of Faculty Development, University of California, Irvine School of Medicine, Irvine, California

Disclosure: Desiree Lie, MD, MSEd, has disclosed no relevant financial relationships.

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