Updated July 18, 2006

Physical Activity: The Magic of Movement

by Patti Geil, M.S., R.D., C.D.E., and Laura Hieronymus, M.S.Ed., A.P.R.N., B.C.-A.D.M., C.D.E.

Medical ID. A diabetes identification bracelet or shoe tag should be clearly visible when you exercise.

Carbohydrate source. People who use insulin or certain diabetes drugs that cause the pancreas to increase insulin production are at risk for low blood glucose, or hypoglycemia, when they exercise. For this reason it is important to carry a source of carbohydrate to raise low blood glucose levels if necessary during and after physical activity. Most people are advised to treat themselves if their blood glucose falls below 70 mg/dl by consuming at least 15 grams of carbohydrate. These foods provide 15 grams of carbohydrate per serving: 3 glucose tablets, 1/2 cup fruit juice, 2 tablespoons raisins.

Because the major effect of physical activity is lower blood glucose levels, monitoring before, during, and after exercise is important. Be sure you are familiar with the symptoms of low blood glucose and the steps for treating it. It is possible to develop exercise-induced hypoglycemia several hours after the activity has ended because your muscles continue to take up glucose from the bloodstream, so be prepared to check your blood glucose level and have a source of carbohydrate available in the hours after exercise.

The effect of activity on your blood glucose level depends on many factors, including the time of day you exercise, the timing and dosage of your insulin or pills, when you last ate, your level of fitness, and the duration and intensity of your exercise session. You may need to eat additional carbohydrate before or during exercise if you plan to engage in vigorous or prolonged activity (lasting more than 45 minutes). In these situations, an intake of 15 to 30 grams of carbohydrate every 15 to 30 minutes should be enough to keep hypoglycemia from occurring. Each person’s reaction to exercise is different, though, so it is important to check your blood glucose level regularly during prolonged activity.

Hypoglycemia with physical activity is generally not as common in people with Type 2 diabetes as in those with Type 1, particularly if they don’t take blood-glucose-lowering medicines. These individuals probably won’t need extra food when participating in physical activity. Indeed, the extra calories can prevent a person with Type 2 diabetes from losing weight and reaching his blood glucose goals.

If a person’s blood glucose level is high before exercising, it may be dangerous to exercise. The ADA recommends that people with Type 1 diabetes avoid physical activity if fasting blood glucose levels before exercise are greater than 250 mg/dl and ketones are present in the blood or urine. They should also use caution if preexercise blood glucose levels are greater than 300 mg/dl and no ketones are present. Ketones are a sign that the body doesn’t have enough circulating insulin. When this is the case, the muscles don’t have access to enough glucose for the extra energy demands of exercise, causing the liver to produce more glucose and the body to break down fat stores for energy. If ketones—potentially toxic by-products of this process—build up in the bloodstream faster than the body is able to process them, a person is at risk for diabetic ketoacidosis, a serious condition that can lead to coma and even death.

People who have Type 2 diabetes, on the other hand, can often exercise safely with elevated blood glucose levels. In fact, since physical activity tends to lower blood glucose, a little exercise may be “just what the doctor ordered.” However, it is still prudent for people with Type 2 diabetes who begin exercise with high blood glucose to check their level after about 15 minutes of activity to see whether it is going up or down.

Go!
If you’ve carefully considered your exercise options and planned ahead for safety issues, it’s time to jump in and begin enjoying the benefits of physical activity. Start your exercise program gradually. Some soreness is common in the early stages, particularly if you have not been physically active in recent years. There are several ways to tell if you are overdoing physical activity while you are exercising. One is to do the "talk test." You should be able to talk comfortably with someone while you are participating in an activity. If you are so short of breath that you can’t converse with your exercise buddy, you need to slow down to avoid becoming overtired or injured.

Also in this article:
Risky Business?
Step It Up!

Patti Geil is a diabetes and nutrition consultant in Lexington, Kentucky. She has written numerous books about diabetes, including Cooking Up Fun for Kids with Diabetes (American Diabetes Association, 2003). Laura Hieronymus is the program coordinator/nurse educator at Drs. Borders & Associates, PSC, an American Diabetes Association–recognized education service in Lexington, Kentucky.

More articles on Diabetes Basics

Statements and opinions expressed on this Web site are those of the authors and not necessarily those of the publishers or advertisers. The information provided on this Web site should not be construed as medical instruction. Consult appropriate health-care professionals before taking action based on this information.