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.).

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.