Ask The Expert
Exercise

You just experienced a confusing but very common phenomenon. Exercise does burn energy, and eventually exercise lowers blood glucose. However, even though it is said that exercise "acts like insulin" and enhances insulin's effect to lower blood glucose, exercise is not insulin. Exercise can only lower glucose when there is enough insulin available in the bloodstream to regulate the liver (what I call "putting a lid on the liver").

Glucose response during exercise: When you begin exercising, your liver produces and releases glucose into the bloodstream, to help meet the increased demand for fuel during your activity. In fact, some people are surprised to complete a strenuous activity only to find that their glucose remained the same before and after the activity. This is of course what the non-diabetic experiences: the glucose remains very constant during and after exercise, because while the liver has released extra glucose, the non-diabetic also has enough insulin to regulate how much glucose the liver releases.

The liver's role during exercise: In a way, your liver "has a mind of its own" and continues to produce glucose while you exercise. If you don't have enough insulin available to help the glucose get into the cells, and to regulate how much glucose the liver releases, then the net effect is that your blood glucose will be higher after exercise. Some people with diabetes will notice a significantly higher glucose rise after more strenuous activity and/or competitive sports; this is because epinephrine (adrenaline) is a hormone released during exercise, stress, excitement, or illness, and its effect is to cause the liver to release even more glucose to supply the body with the needed energy.

Usually, this is a temporary effect, and later the blood glucose will go back to its original level. Furthermore, if you take oral agents or insulin, there is the potential for delayed hypoglycemia (low blood glucose) up to several hours after you exercise, as the muscles replenish the stored glucose that was used during exercise. I won't elaborate on this issue now since, from your question, I'm guessing you are newly diagnosed and perhaps diet controlled.

So, to answer your question, yes, the temporary rise in glucose is likely due to the exercise. However, with regards to not testing after exercise, I would suggest you discuss this with your diabetes educator and doctor. They may want you to test at various times to be able to get a good picture of how your glucose responds to food and activity. Make sure to note in your logbook when you exercised and for how long to make it easier for you to see the effect.