Information, Symptoms, Treatments and Resources


Get Ready to Exercise


When to test your blood sugar for the safest workouts


By Jenilee Matz, MPH

Exercise can offer a whole host of benefits when you have diabetes, everything from weight loss to better glucose control. But you can only get the most out of your workouts when you do them safely, and a crucial step is checking your blood sugar levels. Here's how and when to do it.


  • Before exercise

Test your blood sugar before each workout. Do not exercise if your blood sugar is too low, says Gary Scheiner, MS, CDE, owner and clinical director of Integrated Diabetes Services, LLC, in Wynnewood, PA, which provides coaching and counseling for people with diabetes. The actual number varies among people with diabetes, so ask your doctor what your low limit is. 

Exercising when blood sugar is high is typically not a problem, according to Scheiner. However, if you have type 1 diabetes and your blood sugar is high enough to test for ketones (a chemical the body makes when it’s low on insulin, and that can make you very sick), check for them as directed by your doctor. If ketones are present, you should not be physically active, Scheiner says. Also avoid exercise if you feel sick, whether it’s a fever or just an everyday infection, like a cold.


  • During exercise

Check your blood sugar during exercise, too, if you’ll be active for longer than 30 minutes. Romy Block, MD, an endocrinologist and assistant professor of endocrinology at the University of Chicago, recommends testing blood sugar after 30 minutes of moderate activity, like brisk walking, or after 15 minutes of vigorous activity, such as running. Exercise can cause blood sugar levels to plummet, especially if you work out intensely or for a long time, didn’t eat enough beforehand, or take certain medications. Testing your blood sugar mid-workout helps you learn how exercise affects your levels. If your blood sugar drops too low during exercise, see your doctor. He or she may need to tweak your diabetes care plan.

If you experience any warning signs of hypoglycemia, stop your workout and test your blood sugar right away, says Block. Symptoms of hypoglycemia include dizziness, shakiness, weakness, confusion, and irritability. If your blood sugar is low, treat hypoglycemia as directed by your doctor. 


  • After exercise

Check your blood sugar immediately after exercise and as often as your doctor suggests for the rest of the day. You’re at risk for hypoglycemia for 24 hours after exercising, so testing your levels often is essential.

A smartphone app like Sugar Sense (for Android and iOS) is great way to track your blood sugar levels over time. While tracking your blood sugar is one important step, there's more to exercising safely with diabetes.

Published April 17, 2015. 

Jenilee Matz is a freelance medical writer living in Charlotte, NC. She earned her Master of Public Health degree from the University of South Carolina, and previously worked for the Centers for Disease Control and Prevention.

Reviewed by Nora Saul, MS, RD, LDN, CDE on December 5, 2014.
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