Ask an Expert FAQs — Your Exercise Questions Answered

Q: How long does it take for exercise to affect blood sugar levels? How long can this effect be felt for?

A: Exercise may affect your blood glucose immediately after your exercise or a number of hours after your exercise program have been completed. When beginning or changing your exercise program it is important to test your blood sugar to evaluate its effect. If you are taking insulin or a medication that increases your insulin production (sulfonylureas) you are at risk of having hypoglycemia or low blood sugar reaction when you exercise.

There are a number of variables that affect your response to exercise – the intensity and duration of your exercise, the time of day you exercise, your blood glucose level before exercise, the timing of exercise in relation to the peak and duration of your insulin or oral medications, the timing of your food intake, the amount of carbohydrate, and your level of hydration.

When you exercise your body depends on glucose as a source of energy. This glucose is provided by the amount of available glucose in your blood and stored glycogen in your muscles. You must have sufficient insulin available to move this glucose into your cells if you don't your blood glucose may become elevated instead of lowering after exercise or if you have too much insulin available and not enough glucose you may experience a low blood glucose reaction.

As you can see testing your blood sugar is important in order to gain understanding the effect of exercise on your blood sugar.

Also if you have exercised vigorously you may experience low blood sugars for a number of hours following exercise. If you have depleted your stored glycogen; it will need to be replaced so as you eat your meals the carbohydrate will then be quickly utilized maintaining lower blood glucose levels for a number of hours. It is for this reason exercise is such an important component in the management of your blood glucose.

Kathleen Gold, RN, MSN, CDE

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Last Modified Date: February 25, 2013

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by Nicole Purcell
I have a friend, M, who has diabetes and never, ever tests her bloodsugar before she gets behind the wheel. This has always worried me about her. On Wednesday, she had a bad accident after passing out behind the wheel. She hit another car head on. I thank the universe that no one was killed, but she and the driver of the other vehicle were both badly injured. She's got a long healing road ahead of her, as does the woman she hit. I was talking about the...