If I have diabetes, how can I manage my blood sugar levels after exercise?

Dr. Jack Merendino, MD
Endocrinology Diabetes & Metabolism
The first thing a person needs to do is to establish his or her pattern of glucose variation with exercise because this varies a lot from one person to the next. It’s natural to think that blood sugar goes down with exercise, and if often does. But with intense or competitive exercise, the adrenaline that’s released during the activity will usually raise the sugar. Some people find that they are very high at the end of intense exercise and then have a rapid fall or “crash” in their blood sugars a couple of hours later. 

I suggest that when you start exercising or increase the intensity of your exercise, test your blood sugar at the start of the exercise, at the end and an hour or two afterward. You may need to test during the exercise -- maybe every 30 minutes or so if it’s especially intense -- and you may need to test longer after finishing. Do this a few times until it’s clear what happens to you. Then it will be more clear what to do. If you have a big rise with intense exercise, I don’t usually recommend taking more oral medication or more insulin because the number is likely to fall within an hour or two of finishing and you can cause a severe low sugar reaction by trying to prevent the high. But you may be able to modify what you eat before exercising, especially if you ingested a lot of carbohydrate expecting the number to fall. If you do go down during exercise, you may need to eat before the activity, or you may need to eat at the end to prevent a low sugar. Sometimes people will need to modify their medication regimen to account for exercise. For example, one may need to take less insulin or a reduced dose of oral diabetes medication on the days that he or she is exercising. If you bring your record of what happens to you when you exercise to your doctor, the two you can figure out best how to handle the ups and downs.  
Phil Southerland
During the two- or three-hour window after strenuous exercise it’s crucial to know where your blood sugar is and do constant monitoring. It will be different today than it will be tomorrow. This is something all of our athletes with type 1 must do.

After exercise, the body is going through a lot of hormonal changes. Whatever glucose gets produced in the bloodstream to help with exercise, whatever you eat during exercise that your body doesn’t use during the event, combined with the body’s cortisol production can cause a big spike in blood sugar immediately following exercise for about an hour-and-a-half period. It’s common among all of our athletes to give a bolus immediately following exercise to prevent this post-exercise spike. (Bolus is the term we use to describe delivering insulin.)

At that point, it’s about tinkering with the right number to find out how much insulin you need. To dampen the spike, we will, the second we’re done with exercise, do a bolus of 4 units of insulin. If I want to eat, I would double the insulin I would normally do – but that’s just in that one hour period after exercise. Everyone is a little bit different. The one consistency we’ve seen is the spike immediately following exercise and the drop in blood sugar in the hour and a half post exercise.

Continue Learning about Diabetes


Diabetes mellitus (MEL-ih-tus), often referred to as diabetes, is characterized by high blood glucose (sugar) levels that result from the body’s inability to produce enough insulin and/or effectively utilize the insulin. Diabetes ...

is a serious, life-long condition and the sixth leading cause of death in the United States. Diabetes is a disorder of metabolism (the body's way of digesting food and converting it into energy). There are three forms of diabetes. Type 1 diabetes is an autoimmune disease that accounts for five- to 10-percent of all diagnosed cases of diabetes. Type 2 diabetes may account for 90- to 95-percent of all diagnosed cases. The third type of diabetes occurs in pregnancy and is referred to as gestational diabetes. Left untreated, gestational diabetes can cause health issues for pregnant women and their babies. People with diabetes can take preventive steps to control this disease and decrease the risk of further complications.

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.