Physical Activity & Blood Glucose

Because diabetes a disorder that affects the way your body processes glucose, when you engage in physical activity you need to be especially aware of changes in blood glucose levels as your body burns extra glucose for energy. This can help you avoid problems like low blood glucose (hypoglycemia). Being aware of changes in blood glucose during physical activity is especially important if you take certain diabetes medications that increase risk for hypoglycemia, including insulin or diabetes medications that cause insulin secretion (called secretagogues), including sulfonylureas (glimepiride) and glinides (repaglinide and nateglinide).1

Should I avoid physical activity if my blood glucose is very high

In general, if your blood glucose is very high (250 mg/dL) and you take insulin, you should avoid vigorous physical activity. However, if your blood glucose is mildly elevated and you feel well, you may exercise safely. Remember, make sure to drink water so that you are adequately hydrated before, during, and after any physical activity. Dehydration can affect your blood glucose.2

How should I monitor blood glucose during exercise?

Even if you do not use insulin or a diabetes medications called secretagogues that increase secretion of insulin (this includes sulfonylureas [glimepiride] or glinides [repaglinide and nateglinide]) to control your diabetes, you may still want to use a blood glucose monitor to find out how your exercise routine affects your blood glucose level. Physical activities of long duration and low intensity typically cause blood glucose to decrease, but not to a problematic level. Try monitoring before, during, and after training several times so that you understand and anticipate exercise-related changes in blood glucose. Although exercise-related hypoglycemia is uncommon in people with diabetes who control their diabetes with lifestyle modifications alone or use diabetes medications other than insulin or secretagogues, if you find that your blood glucose gets too low during exercise or if you exercise for a long period of time or at a high-intensity level, plan to have a snack before you start exercise, or during or after you exercise.1-2

If you take insulin or a secretagogue, you should measure your blood glucose before exercise. If the level is under 100 mg/dL, you should have a snack (15 grams of carbohydrate) before starting physical activity. When you finish exercising, make sure to take a blood glucose measurement. After exercising, your blood sugar may continue to drop because the body is using available blood glucose to replenish its store of glycogen. You may want to try eating some carbohydrate after exercising to compensate for this after-exercise decrease in blood glucose If you engage in high-intensity or long duration physical activity, to prevent post-exercise hypoglycemia, take 5-30 grams of carbohydrate during physical activity and within 30 minutes of finishing.1

If you take insulin, keep in mind that the most common cause of exercise-related hypoglycemia is not getting adequate carbohydrate intake before, during, and after physical activity.2

Should I adjust my insulin dose when I’m exercising?

If you take insulin to control your diabetes, speak with your healthcare provider about whether you should adjust your insulin dose when you exercise. If your provider recommends that you adjust your dose of insulin to compensate for the effects of physical activity, he or she will work with you to develop a strategy for adjusting the dose.

Whether you should adjust your insulin dose due to physical activity will depend on the kind of insulin regimen you are using. If you use a fixed regimen of insulin, that is if you take insulin at the same times every day, you should schedule your training at the same time every day to help you maintain predictable blood glucose levels.

If you use a more flexible insulin regimen, your healthcare provider may want you to adjust your insulin dosing depending on how physical activity affects your blood glucose level. One rule of thumb is to reduce the dose of insulin you take closest to your training time by about 30%. Decreasing your insulin dose is most important for people who exercise for a long period of time (over 60 minutes).3

Learn more about different insulin treatments

How long after physical activity will my blood glucose be affected?

Physical activity can affect blood glucose levels long after you’ve finished your workout. In fact, your blood glucose may continue to decrease up to 16 to 24 hours after you have finished exercising, depending on how long you exercised and your intensity level. This is because the glucose stored in our muscles is used first for energy when we exercise. After you exercise, your body will take glucose out of your bloodstream to replenish these glucose stores, resulting in lower levels of blood glucose. This is why if you exercise later in the day, you may increase your risk for hypoglycemia during sleep. Always make sure you consume enough carbohydrates to compensate for the glucose that is burned during physical activity. Try monitoring your blood glucose after physical activity and before sleep so that you have a good idea how activity affects your blood glucose.4

Does physical activity affect the location of my insulin injection?

When it comes to insulin and physical activity, the location of your insulin inject is another important consideration. Insulin is absorbed more quickly by the muscles that are directly involved in physical activity. Therefore, to prevent increased absorption, find a site on your body that does not include muscles that you’ll be using during your workout. For example, if you are bicycling, your arm (and not your leg) is a good location for an insulin injection. If you are using your arms during your activity (such as in playing tennis or racquetball), try injecting in your abdomen. Even though insulin absorption from the abdomen area is generally faster than from the limbs when you are at rest, the difference can be reversed when you are performing physical activity that uses the arms or legs.3

What should I do if I feel like my blood glucose is low during physical activity?

If you feel like your blood glucose may be too low during physical activity, stop immediately and take 15 to 30 grams of carbohydrate. Hypoglycemia can be dangerous, so don’t try to keep exercising. If you feel that your blood glucose is too low, listen to your body and take immediate steps to correct your blood glucose. Always have carbohydrates on hand when you exercise. Fruit juice or a soft drink is a good option because it will give you sugar as well as water. Remember to drink to get enough liquid before, during, and after physical activity. Dehydration can affect your blood glucose.1

Learn more about hypoglycemia

Can physical activity increase my blood glucose?

Even though the main concern with physical activity and blood glucose is hypoglycemia, physical activity can cause blood glucose levels to rise. This can happen when your body has an insufficient amount of available insulin and you exercise intensely. During vigorous exercise, the body sends a signal to the liver to release glucose that is being stored. Without sufficient insulin, this flood of glucose can cause a rapid rise in blood glucose. Without the ability of using this glucose, the body may burn fat for energy, leading to production and build-up of ketones and risk for ketoacidosis.4

Learn more about ketoacidosis.

Written by: Jonathan Simmons | Last reviewed: May 2014.
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