Information alert

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Being active is an important part of a healthy lifestyle. Being more active or training for a sport may make blood glucose levels harder to manage at times. You need to know how to adjust insulin and when to eat when you are being active. This information sheet will help you to understand how to keep your blood glucose levels stable during activity.

What happens to blood glucose levels during activity/exercise will depend on the balance between:

  • Type of exercise (intensity)
  • Timing of exercise (when and how long)
  • The amount of insulin on board
  • Your food and fluid intake

Different types of exercise will have different impacts on your blood glucose levels. This is why it is very important to check blood glucose levels often.

Exercise which is aerobic usually lowers blood glucose levels (examples include, running, cycling walking, swimming), exercise which is anaerobic (examples include sprinting, weight training, strength and power sports) usually push glucose levels up. Mixed activities like team sports may lower or increase blood glucose levels.

Figure adapted from Riddell et al The Lancet Diabetes & Endocrinology 2017 5, 377-390DOI: (10.1016/S2213-8587(17)30014-1

  • Aim to keep your blood glucose levels between 5 and 10mmol/L. The best range for performance is 6-8mmol/L.
  • If blood glucose is below 3.6mmol/L treat and bring above 5mmol/L before starting exercise
  • Use your blood glucose level as a guide to when and how much to snack, before and during exercise.
  • Check blood glucose levels before exercise and every 30minutes during exercise
  • If blood glucose level is above 10mmol/L and exercise pushes the blood glucose levels up avoid disconnecting the pump if possible or give a half correction
  • If blood glucose levels are above 10mmol/L and rising a half correction may be needed during anaerobic or competitive exercise
  • If blood glucose is 14mmol/L or more check for ketones and follow your ABC rules
  • Do not exercise if ketones are >1mmol/L, give a correction and wait for ketones to drop below 0.6mmol/L. If ketones are between 0.6mmol/L and 1mmol/L give a half correction and begin exercise

Hypos before exercise

If you have a hypo in the hours before you exercise, you are more likely to have a low blood glucose level during exercise. Monitor your blood glucose levels closely during exercise

  • Insulin is usually lowered to reduce the risk of hypoglycaemia during aerobic exercise.
  • Anaerobic exercise may not need insulin adjustments.
  • Low insulin levels can cause high blood glucose levels during anaerobic or competitive exercise.

For planned aerobic exercise up to 2hours after a meal or snack with insulin

  • Reduce your pre exercise meal or snack insulin.
  • Start with a 25% reduction for aerobic exercise that lasts up to 45minutes and a 50% reduction for aerobic exercise that lasts longer than 45minutes.
  • Remember this is a starting guide; adjust according to responses to blood glucose responses during exercise.

If you use an Accu-Chek Expert meter programme these reductions in the health settings.

  • Unplanned activity after a meal usually means that the insulin dose at the meal has not been reduced. This increases the risk of a low blood glucose level.
  • Check blood glucose levels before activity.
  • Aim for a blood glucose level between 5 and 8mmol/L
  • Use the exercise snacks and blood glucose guide below to decide how much extra carbohydrate may be needed to prevent a low blood glucose level.
  • If blood glucose is raised do not give a correction unless blood ketones are >0.6mmol/L

  • Use the information available from smart blood glucose meters before and during exercise to check how much active insulin is present.
  • If your blood glucose levels before and during exercise are ok (5-8mmol/L) and active insulin is present you will need to have an extra carbohydrate snack.

High glucose levels after exercise

  • Sometimes blood glucose levels can increase immediately after exercise.
  • If this happens, you should manage them carefully as a high blood glucose levels at the end of exercise may drop without extra insulin.
  • If extra insulin is needed give no more than a half correction dose.
  • If exercise has been intense or very competitive then high blood glucose levels may be due to high lactate levels. A cool down will help to get rid of lactate and this will help to lower blood glucose levels.

Low Glucose Levels after exercise

  • All types of exercise can lower blood glucose levels for up to 24 hours after you stop being active. This is called late onset post exercise hypoglycaemia (LOPEH).
  • After exercise your muscles and liver use up more glucose to replace the stores that have been used. It is easier for glucose to enter muscles without insulin after exercise so you may be more sensitive to your insulin and need to reduce your night time background insulin doses.

If any type of activity takes place in the afternoon or evening reduce background insulin by 20% before bed to reduce the risk of low blood glucose levels at night. Check blood glucose levels at 2- 3am.

During exercise, you may need additional carbohydrate to prevent low blood glucose levels. If you do more than 60minutes of exercise then you are more likely to need additional carbohydrate for fuel.

Carbohydrate during exercise
Exercise snacks need to be easy to eat and low in fat so you don’t get too many extra calories. Use the exercise snacks guide, which is available on the website to decide how much you need to eat during exercise

Remember to drink during activity/exercise especially in hot weather and if blood glucose levels are raised.

  • For activities lasting up to 60minutes drink water
  • For activities lasting longer than 60minutes a drink with carbohydrate may be useful

After exercise, it is important that you eat enough carbohydrate and protein to replace the fuel used by your muscles. Eating well after exercise will help prevent low blood glucose levels after exercise. Try and eat within 1-2hours of activity that has lasted 60minutes or longer, this maybe your next meal or snack. If the activity is between your evening meal and bedtime then always have a bedtime snack. Food eaten up to 4-6hours after all types of exercise usually needs 25-50% less insulin than usual.

You can contact the Childrens Diabetes Dietitians via or on 020 3447 2424

You can find expert advice and information about children and young people's type 1 diabetes at

Page last updated: 10 May 2024