Managing Blood Sugar When Exercising

Safe blood glucose ranges for exercise for people with diabetes.

If you have plans to exercise and have diabetes, this article is for you. Use this guide as a reference to help you stay safe on your journey to a healthier you!

Consult With Your Doctor First

Any significant changes should be discussed with your doctor, especially changes in diet and exercise. These two categories can significantly affect your blood sugar and how your body responds to medications.

Always discuss exercise with your doctor BEFORE starting any kind of exercise program. This is especially important if you are on medications. Full disclaimer here.

These guidelines are most applicable to people with type 1 diabetes, LADA, or another insulin-dependent type of diabetes. If you have prediabetes or type 2 diabetes, discuss with your doctor which of the below measures you should take when exercising.

Safe Blood Sugar Ranges

Only begin exercising if your blood sugar level meets the following criteria. During exercise, if your blood sugar falls outside of this range, stop exercising.

Before Exercise

Don’t start exercising if your blood sugar is:

  • Over 250 mg/dL (13.9 mmol/L)
  • Under 100 mg/dL (5.6 mmol/L)

During Exercise

Make sure your blood sugar levels stay above:

  • 70 mg/dL (3.9 mmol/L)

What Items to Have on Hand

If you plan on exercising for at least 30 minutes or you are away from the house while exercising, it is important to have some fast-acting carbohydrates with you so that you can consume 15 grams of carbohydrates when/if needed.

Fast-acting carbohydrates include:

  • Glucose tablets (4 pieces = 16g)
  • Fruit juice (depends on the fruit juice)
  • Skittles (15 pieces = 15g)
  • Starburst chews (4 pieces = 16g)
  • Jelly Belly jelly beans (15 pieces = 15g)
  • Brach’s jelly beans (7 pieces = 15g)
  • Welch’s fruit gummies (0.8 ounce pouch = 17g)
  • Sour Patch Kids (5 pieces = 15g)
  • Large marshmallows (2 pieces = 12g)
  • Gummy Bears (5 pieces = 15g)
  • Gummy Life Savers (5 pieces = 15g)
  • Gushers (0.9 ounce pouch = 20g)
  • Candy Corn (8 pieces = 15g)

Be Safe!

Stop exercising immediately if your blood sugar levels fall below 70 mg/dL (3.9 mmol/L) or:

  • You feel lightheaded, dizzy, or disoriented.
  • You gain blurred vision.
  • You start to feel shaky or anxious.

Stop exercising immediately if your blood sugar levels rise above 250 mg/dL (13.9 mmol/L) or:

  • You feel nauseous or vomit.
  • You have difficulty breathing.
  • You have ketones in your urine.

When to Avoid Exercise
If your blood sugar is above 250 mg/dL, we recommend putting off exercise until your blood sugars are consistently below this level. These lower levels can be obtained by focusing on diet and sleep first.

Why to Avoid Exercise over 250 mg/dL
Ketones are substances made when stored fat is broken down for energy. The presence of ketones indicates that your body doesn’t have enough insulin to control your blood sugar. When ketones are quickly produced, they can cause Diabetic Ketoacidosis (DKA). DKA is a serious, sometimes fatal, condition that requires immediate medical treatment.

Although it can be feasible to exercise if your blood sugar is over 250 mg/dL, it can be potentially dangerous. If you exercise when you have high blood sugar and ketones present, you risk DKA as the ketones will cause your blood sugar level to rise even higher.

If your blood sugar is above 250mg/dL, you need to test your urine for ketones using an over-the-counter ketone test kit (available at most pharmacies or drug stores.) If ketones are present, do not exercise. If ketones are absent, we recommend consulting with your doctor before exercising.

Read this article by the CDC to learn more about Diabetic Ketoacidosis.

15-15 Rule

Be sure to check your blood sugar every 30 minutes of exercise, as certain types of exercise can drastically change your blood sugar.

If your blood sugar falls below 70 mg/dL (3.9 mmol/L), stop exercising immediately and follow the 15-15 rule:

  • Consume about 15 grams of fast-acting carbohydrates.
  • Wait 15 minutes and recheck your blood sugar.

While blood sugar levels are below 100 mg/dL (5.6 mmol/L), repeat this process. Once your blood sugar levels are over 100 mg/dL (5.6 mmol/L), it is safe to continue exercising.

Strenuous Exercise and Extended Exercise

If you are participating in strenuous exercise, such as weight lifting, resistance training, sprinting, or HIIT (high-intensity interval training), you will likely find your blood sugar level spikes during exercise. This is because of the blood sugar raising hormones released during intense exercise.

Moderate exercise, such as brisk walking, dancing, biking, and swimming, usually does not raise blood sugar levels. Most often, you will find your blood sugar level lowers with these activities. However, if you participate in moderate exercise for extended periods, you may see your blood sugar spike. This usually happens after 2 hours of continuous moderate exercise.

While this spike is only temporary, it is important to know this may occur. If you have type 1 diabetes or LADA, you may need to adjust your insulin during or after your workout accordingly. Be sure to discuss your exercise plan with your doctor so you can have a plan for adjusting insulin and medications.

Learn More

If you are unsure how your blood sugar might respond to certain types of activity, please check out our article, Exercises to Lower Your Blood Sugar which details how different activities affect blood sugar.