How does diabetes affect exercise?

If you’re going to exercise, you need to see how it affects your blood sugar. We usually recommend that patients with diabetes take their blood sugar before they exercise, and then take it again afterwards so they’ll understand what exercise does to their blood sugar.

Bob Greene
Bob Greene on behalf of The Best Life
Physiology Specialist

Having diabetes or prediabetes changes one important response to exercise—the way your body adjusts the level of glucose, which is needed to power your workout. It boils down to the way diabetes alters insulin and other hormones that control blood sugar.

Here's what's supposed to happen during exercise: At the beginning of a workout, muscles use mainly glucose, pulled from the blood, and glycogen (the stored form of glucose in muscles). As the workout progresses, the fuel shifts to a mix of glucose and fatty acids. Insulin, as you know, plays a key role in ushering glucose into muscle cells. During exercise, insulin needs to be available to help sugar get into your cells, but must also keep a low profile because a high level of insulin in the blood tells the liver not to release glucose—glucose you need to keep your energy up.

In a person without diabetes, insulin ebbs and flows as the body needs it. But when you have diabetes, several things can throw this system off. In one case, you don't make enough insulin, so you can't get enough sugar into your cells and you start feeling pretty tired on the treadmill. Or you're taking insulin or a medicine that revs up insulin production and you have too much insulin in the bloodstream, which tells the liver to stop releasing sugar just at the time you need it most. That can cause a hypoglycemic reaction.

Normally, with vigorous exercise, the body releases several other hormones. The main one is adrenaline, also called epinephrine. Adrenaline is the body's "fight-or-flight" hormone. It causes your heart rate to go up, increases blood flow to the muscles, enhances breathing, and generally prepares you for a burst of physical activity. That increased activity requires fuel, so adrenaline also causes the release of glucose into your bloodstream from the glycogen in your liver. So when you step out onto the tennis court, your blood sugar level may actually go up after you start to play.

The Best Life Guide to Managing Diabetes and Pre-Diabetes

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The Best Life Guide to Managing Diabetes and Pre-Diabetes

Bob Greene has helped millions of Americans become fit and healthy with his life-changing Best Life plan. Now, for the first time, Oprah's trusted expert on diet and fitness teams up with a leading...

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.