Inside your body

Inside your body

To understand how exercise affects your blood glucose levels and how you can adjust your food and insulin intake to prevent highs and lows, it’s useful to look at what happens inside your body when you take exercise. 

What happens when I exercise or increase my activity levels? 

When you exercise, you need more energy, otherwise, you will struggle to cope with the increased demands on your body.  If there is too much insulin and not enough glucose/carb, then hypoglycaemia is a real risk during exercise.  

However, you also need insulin on board during exercise to move the glucose into the muscles. It is possible for glucose levels to rise during exercise if your body does not have enough insulin in the system. 

What about hypos after I exercise? 

Hypos are common with exercise and can happen even up to 24 hours after. These occur because your metabolic “glucose-burn” rate increases and remains elevated after exercise.

What happens if I have a hypo?

If you are having a hypo when exercising you must stop. You should treat your hypo with glucose in the usual way (i.e. with Dextrose tabs, Lucozade, Jelly Babies, etc.).

common quick acting hypo treatment foods, fruit juice, cola bottle sweets, sugar sweets 20g carbs each
Some common quick-acting hypoglycaemia treatments

You may also need slowly absorbed carbohydrate. Afterwards, think about the following points to reduce the risk of having another hypo. 

  •  Regular monitoring of your blood glucose in the hours after exercising will help detect any further hypoglycaemia.
  • If your hypo occurred within 90 mins of your last meal and bolus dose, then next time think about reducing the bolus insulin dose or taking some extra carbohydrate before exercising. 
  • If you had a hypo after exercising, you may wish to eat a carbohydrate-based snack at the end of your exercise session.
  • If you had a hypo during the night after exercising, consider taking an extra 20–40 g carb snack at bedtime (with no insulin) or taking less bolus insulin with your evening meal. 
  • It may be useful to check your blood glucose during the night if you have exercised in the evening, as evening exercise can cause nighttime hypos.  


  1. Comment by Samantha. C. on 30th April 2020 at 7:37 am

    I found that my blood sugar change reacts very quickly when exercising therefore I’m at risk of running low. Every morning when I first get up I do a brisk walk for half an hour with my dog. I test my blood sugar before I go,out and depending on that reading depends how much change I would make to my temp basal on my insulin pump. e.g. if I was say 5.9 I would suspend it completely for half an hour I.e. no insulin being administered at all. After half an hour my pump will bleep to remind me it needs returned back to normal. It has been known for me still to have a low after my walk therefore I would set it to suspend my insulin maybe 10 or 15 before I do my walk.
    When I used to swim. My target always was 20 lengths of the pool which normally I could do in half an hour so again I would suspend my insulin for half and hour. Through out the day I would also do some extra blood sugar tests as later on in the day sometimes I was at risk of runing low depending what I was doing after my swim.
    Over time you learn how your body reacts to exercise when taking insulin.
    Very interesting topic.

  2. Comment by Kirsten. C. on 12th May 2020 at 2:21 pm

    Great to hear about your exercise routine and how you balance that with your glucose levels. You’re right, over the years you do figure out how your body reacts to different forms of exercise and adjust accordingly.

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