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When, How and Why You Should Check Your Blood Glucose During Exercise

An important part of managing diabetes is staying active and exercising. And while exercising plays a key role in helping you control your diabetes, checking your blood glucose before, during and after exercise is just as important.


One concern during exercise is low blood glucose (hypoglycemia), so monitoring your blood glucose is very important. Your muscles and liver store glucose that is used up during exercise. While the body works to replenish the glucose it stores away, it will borrow glucose from your blood. The longer and harder your workout, the more the glucose in your blood will be affected. Your blood glucose levels can also go up during exercise, especially if you're doing short bursts of intense exercise.

This is why you might need to check your blood glucose level 30 minutes before starting a workout and again immediately after exercising. During workouts that last over 60 minutes, stop to check your level every half hour, especially if you're trying a new exercise or increasing intensity. If you are a beginner, it is not recommended to exercise for longer than 90 minutes because you may run the risk of hypoglycemia. However, if you do exercise more than 90 minutes (if you're on a long hike, for instance), make sure you monitor your blood glucose more often than you would normally. Also, keep fast-acting carbohydrates on hand in case your blood glucose goes under 4 mmol/L.

You should stop exercising if:

  • Your blood glucose is 4.0 mmol/L or lower
  • You feel shaky, nervous or confused

To raise your blood glucose level, eat or drink 15 g of carbohydrates (glucose), such as:

  • 15 g of glucose in the form of glucose tablets
  • 15 mL (3 teaspoons) of table sugar dissolved in water
  • 3/4 cup of juice or a regular (not diet) soft drink
  • 6 Life Savers candies
  • 15 mL (1 tablespoon) of honey

Check your blood glucose again 15 minutes later. If your blood glucose level is still under 4 mmol/L, repeat. If your blood glucose level is over 4 mmol/L, eat your next meal, or if your meal is more than one hour away, eat a snack containing a carbohydrate and a protein (for more information, read the article on how to manage hypoglycemia):

Sample carbohydrates:

  • A slice of bread
  • ½ cup of cereal
  • 7 crackers

Sample protein:

  • A piece of cheese
  • ¼ cup of nuts
  • 2 tbsp. peanut butter

Once your blood glucose level is over 4 mmol/L, you need to eat something within the hour. If you have a meal coming up, then you don't need to worry. However, if you won't be eating a meal within an hour, eat a snack containing a carbohydrate and protein to tide you over until your meal.

You may need to check your blood glucose immediately after exercising and several times over the next few hours. It's possible that your blood glucose could remain low for 24 to 48 hours after exercising.