DOCTOR'S VIEW ARCHIVEMedical Author: Ruchi Mathur, M.D.
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR
Part 1 of this Diabetes and Exercise discussion focused on the benefits of exercise for patients who have diabetes . In this section, we will review specific concerns regarding diabetes and exercise and what you should be aware of as you try to maintain a healthy lifestyle.
Hypoglycemia is a condition that occurs when blood sugars fall to excessively low ranges (usually less than 60mg/dl). With hypoglycemia, patients experience confusion, sweating, shakiness, and in severe cases, coma and seizure. Exercise can induce hypoglycemia, particularly in patients who are taking insulin, although patients on oral agents are also at risk. In part, this decrease in blood sugar results from an increase in the muscles' use of glucose and because the liver's production of glucose is impaired.
Studies have shown that patients taking insulin who reduced the dose of their short-acting insulin by 33 to 50% before exercising were able to prevent the onset of exercise-related hypoglycemia. While hypoglycemia can occur during or directly after activity, it can also occur 6 to12 hours after exercise. Caution is therefore recommended during this period as well.
For patients who exercise regularly and need insulin therapy, an insulin pump is a great option for delivery. The pump provides a constant infusion of insulin that can be adjusted and allows for an extra amount to cover meals. With the aid of a doctor or nurse trained in pump therapy, the dosing can be adjusted to fit exercise regimens. The only activities for which the pump may not be well suited are swimming and sports involving vigorous movements. These activities can dislodge the cannula, the tube through which the insulin is infused into the body.
Some strategies to avoid hypoglycemia are listed below:
- Measure blood sugars before, during, and after exercise.
- For planned exercise, if you are on insulin, reduce the short-acting insulin by 33 to 50%.
- For unplanned exercise, take 30 to 20g of carbohydrates extra for each 30 minutes of exercise.
- Avoid injecting insulin into the arms and legs and use the abdomen because the insulin will be absorbed more evenly.
- If you exercise in the evening, you may need to add a snack before bedtime to make certain your sugars don't go too low at night.
Diabetes, Exercise, and Small Blood Vessel Disease
Patients with diabetes often have eye disease, whether they have symptoms or not. The eye disease associated with diabetes results from the formation of small, fragile, easily breakable blood vessels in the back of the eye (retina). When these vessels break, bleeding in the back of the eye occurs. Continued damage can result in loss of vision.
In patients with extensive eye disease related to diabetes (diabetic retinopathy), the intensity and type of exercise may need to be limited. Activities that should be avoided include excessive straining (as in weight lifting), excessively jarring activities (such as boxing), and exercise that involves severe pressure changes (like diving). If there is early eye disease and no new vessel formation, no limitations are necessary. If kidney disease is present, the only precaution is avoiding exercise that can raise blood pressure.
Diabetes, Exercise, and Large Blood Vessel Disease
Large blood vessels, such as those that normally supply blood and oxygen to the heart, can also be affected by diabetes. A careful medical history and examination are needed in all diabetic patients who have heart disease before they commit to an exercise program. From a recent Consensus Development Conference on the diagnosis of Coronary Heart Disease in people with Diabetes, the American Diabetes Association has published recommendations for exercise stress testing in diabetes patients. Stress testing should be done before embarking on an exercise program.
The recommendations of the American Diabetes Association for testing are listed below:
- Any patient with cardiac symptoms.
- Abnormal resting EKG.
- Peripheral or carotid artery disease.
- Sedentary lifestyle, age > (greater than) 35 years, and plans to begin a vigorous exercise program.
- Two or more of the following risk factors in addition to diabetes:
- Total cholesterol > 240mg/dl, LDL.160mg/dl, or HDL <35mg/dl;
- Blood pressure > 140/90;
- Family history of premature heart disease; and
- Kidney involvement from diabetes.
What does this mean for you?
Before starting on any exercise program, a through examination and medical history should be performed by your doctor. Patients who have diabetes should pay particular attention to blood vessel complications. Another important area to discuss is the estimated calorie expenditure and strategies to lessen the risk of hypoglycemia. Food intake both before and after exercise should be reviewed. Because approximately 50% of the calories burned during exercise come from a carbohydrate source (with the remainder coming from fat), you can calculate that in a 30 minute exercise session, wherein an activity like cycling at 8mph burns about 10 cal/min, a person would need to consume about 38g of carbohydrates (50% of 300kcal =150 kcal or 37.5 g of carbohydrate). We know this because each gram of carbohydrate is 4 kcal, and 150 divided by 4 is 37.5). These calculations, while a little confusing at first, can be a really valuable tool with some practice and guidance.
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Regarding aerobic activity, training sessions should begin slowly. Allow 8 to 12 weeks to reach a desired training level. At a minimum, three to four 20 to 30 min sessions are needed to see a benefit. To estimate your predicted maximal heart rate: take 220 and subtract your age in years. You should be working at about 60 to 70% of this maximum rate to ensure a safe, effective workout. For example, if you are 40 years old, calculate as follows: 220 - 40 =180 and 70% of 180 = 126. This means your heart rate should be up to 126 beats per minute. It is also important to remember to add a warm up and cool down period to your workout to help prevent injury.
In addition to the above information, the American Diabetes Association has made the following recommendations for exercising:
- Carry an ID card and wear a bracelet that identifies you as having diabetes.
- Be alert for signs of hypoglycemia during and after exercise.
- Drink plenty of fluids before, during, and after exercise.
- Measure blood sugar levels and act if the reading is less than 80mg/dl or greater than 240mg/dl.
I hope the above information provides you with useful guidelines to exercising and living healthy with diabetes. If you need more specific information, the American Diabetes Association web site is a great resource (http://www.diabetes.org) and the International Diabetic Athletes Association has additional information. These organizations can be reached by calling (602) 433-2113.
Once again, discuss any question or concerns you may have with your physician before
starting any activity program. When done safely, there is no doubt that the
benefits of exercise in patients with diabetes far outweigh the risks. (Note:
Gary Hall, now famous an an Olympic Gold Medalist is swimming, is an
To read Part One of this series, please see Exercise Therapy in Type 2 Diabetes: Part 1 - The Benefits.