Leaflet Details
| Title | Exercise and Insulin |
| Department | Diabetes / Dietetics |
| Author(s) | Diabetes Dietitian |
| Review Date | December 2023 |
| Next Review | December 2025 |
| Download | A5 Booklet PDF |
| Accessibility Options | Click on the Recite Me button to show our accessibility resources |
Patient Information
Effects of Exercise on Blood Glucose Levels
Different types of exercise may affect your blood glucose levels in different ways. Testing blood glucose levels before, during and after exercise will help you identify how your body responds and how best to manage the effects.
Low blood glucose levels may be caused by:
- Increased uptake of glucose into the exercising muscles to provide energy during and after exercise
- Faster insulin absorption due to increased blood flow- avoid injecting into exercising muscles
- Too much circulating insulin / insufficient carbohydrate ingestion
- Increased insulin sensitivity for up to 24 hours post exercise - increased risk of hypoglycaemia for all types of exercise.
Increased blood glucose levels may be caused by:
- Too little circulating insulin to allow glucose uptake into muscle cells
- Hormone responses increase glucose production from the liver
Type and Intensity of Exercise
Aerobic
Longer duration, moderate intensity endurance (more than 30 minutes) e.g. brisk walking, running, swimming, cycling.
- Greater risk of hypoglycaemia during and after exercise
Anaerobic
Short duration, high intensity (no more than a few minutes) e.g. sprinting, weightlifting.
- Greater risk of hyperglycaemia during and immediately after exercise
Intermittent high intensity
Lots of sports have periods of low or moderate intensity activity punctuated by bursts of high intensity e.g. football, netball.
- Less immediate risk of hypoglycaemia, possible hyperglycaemia
Variables which can cause hypoglycaemia
- Repeated episodes of exercise
- Recent hypoglycaemia (within last 24 hours)
- NB. Do not exercise within 24 hours of an episode of severe hypoglycaemia
- Changes in weather temperature
- Altitude
Variables which can cause hyperglycaemia
- Competition stress
- Heat stress including humidity
- Dehydration
- High blood glucose pre-exercise
Blood glucose (BG) levels at the start of exercise
| BG mmol/l | Action |
| <7 mmol | Consider having some carbohydrate |
| 7-12 mmol | Exercise may be started |
| >12-16 mmol (no ketosis) | Delay carbohydrate during exercise until BG reduces. Mild to moderate aerobic exercise e.g. light jogging / walking may commence with regular BG monitoring |
| >16 mmol (no ketosis) | Delay exercise until BG falls to safe level especially if planning intense exercise - BG may rise further |
| Ketosis | Delay exercise until ketones cleared |
BG monitoring
- Before exercise
- Every 20-30 minutes during
- At the end of exercise
- Ideally, later on as well
Use this information to decide whether changes in insulin doses or carbohydrate intake are necessary.
Carbohydrate intake
*Before exercise
Ensure you have had some moderate GI (Glycaemic Index) carbohydrate 1-2 hours before e.g. hummus and crispbreads, banana, and almonds.
During
For moderate intensity endurance exercise, quickly digested (high GI) carbohydrate may be required after 20 minutes of exercise in an amount of 30-60g spread across an hour. Have fluids- dehydration leads to poor performance.
Lower intensity or intermittent high intensity exercise may need smaller quantities or none at all.
Immediately after exercise
Foods / drinks containing high GI carbohydrates should be available as soon as possible after exercise. Proper rehydration is essential.
Your dietitian will be able to help you with this and provide information about the Glycaemic Index.
*Planned exercise - insulin dose adjustment
If you are undertaking moderate intensity endurance exercise within 90 minutes of a meal, consider reducing the meal insulin bolus. As people respond differently to exercise, it is not possible to give exact guidelines, but it is best to start with a small reduction, e.g. 20%, and monitor results. Discuss changes to your basal insulin with your healthcare professional.
Unplanned exercise - carbohydrate supplementation and diet
Unplanned exercise may need additional carbohydrate intake.
Consider:
- Pre exercise blood glucose level
- When was your last meal / insulin bolus?
- Type / duration of exercise
Post exercise
There is an increased risk of hypoglycaemia for up to 24 hours post exercise. Monitoring blood glucose levels and noting trends in glucose fluctuations will help you avoid this. You could:
- Reduce your post exercise meal bolus
- Have a carbohydrate rich snack after exercise (without extra insulin), particularly if exercising in the evening
General safety
- Always ensure you have some fast-acting carbohydrate with you in the event of hypoglycaemia
- Remember to take your blood glucose monitor with you
- Carry some form of diabetes identification and, if possible, let other people know how long you will be
- Wear appropriate footwear
- Stay hydrated
Useful websites
Runsweet
https://www.runsweet.com/
Diabetes UK
https://www.diabetes.org.uk/
American Diabetes Association
https://diabetes.org/
