Exercise and Physical Activity: the Impact on Blood Glucose
Contents
How will physical activity affect my blood glucose?
The effect of physical activity on blood glucose depends on the type, intensity, duration and frequency of the activity. Your blood glucose level before you start physical activity, how it is changing and your underlying fitness will also have an influence.
What are the types of physical activity?
Exercise can be broadly divided into:
• AEROBIC (increase your heart rate and breathing)
• ANAEROBIC (short, fast, high-intensity activities that do not use oxygen),
• FLEXIBILITY
• MIXED.
The figure below shows examples of different types of physical activity and how they affect blood glucose levels:
What is the intensity of an activity?
Different types of physical activity affect your blood glucose levels in different ways — and a key factor is how intense the activity is.
Exercise intensity refers to how much energy your body uses during an activity. This is measured by how many calories you burn.
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Lower-intensity exercise, like walking, uses more energy from fat because your body doesn’t need to produce energy quickly and efficiently to maintain the activity. For example, if you walk a mile, about 80% of the energy comes from fat and 20% from glucose.
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Higher-intensity exercise, like running, uses more energy from carbohydrates. That’s because your body needs to produce energy quickly, so glucose becomes the main fuel. If you run a mile at a hard pace, around 80% of the energy comes from glucose.
The higher the intensity of the exercise, the greater the impact it will have on your blood glucose level.
Measuring the intensity of an activity
There are several ways to measure the intensity of a particular form of exercise:
The Talk Test
Low-intensity activity
You should be able to carry on a conversation during the exercise
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- Walking at a casual pace
- Cycling at a casual pace
- Stretching routine
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Moderate-intensity activity
You will be able to talk but not sing during the exercise
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- Brisk walking
- Water aerobics
- Cycling (flat surface)
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High-intensity activity
You will not be able to say more than a few words without pausing for a breath
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- Running
- Fast swimming
- Football, rugby, netball or hockey
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Perceived exertion
The Borg Rating of Perceived Exertion (RPE) scale is a simple way to measure how hard you're working during physical activity. It’s based on how you feel while exercising — known as your perceived effort.
You might notice signs like:
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A faster heartbeat
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Heavier breathing
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Sweating
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Tired or aching muscles
Try to rate your effort as honestly as you can — don’t overestimate or underestimate how hard it feels. Focus on your own experience, not how others might feel doing the same activity.
Take a look at Table 1 for the scale and descriptions, then use it to rate your effort during exercise.
💡 Most healthy people aim to stay at an intensity level between 12 and 16 for general fitness.
Does it matter how long I exercise for?
The longer you exercise, the more the effect on blood glucose levels. Most people cannot maintain high-intensity anaerobic activity for prolonged periods, so generally longer periods of activity are more likely to lower blood glucose.
For people taking insulin or some tablets (sulphonylureas such as Gliclazide or meglitinides such as Repaglinide), there is a risk of hypoglycaemia if you exercise for longer.
30 minutes or less:
Has a minimal effect on blood glucose as the muscles use the glucose stored in the muscle
More than 30 minutes:
There is a risk of hypoglycaemia as the muscles use up the glucose from the blood
Blood sugar monitoring
The only way to know the effect of exercise on blood glucose levels is to monitor blood glucose. However, not everyone needs to do so.
Diabetes Management Approach |
Examples |
Need to Monitor Blood Glucose? |
Reason |
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Diet and exercise only (no medication) |
N/A |
No |
Exercise is unlikely to cause significantly high or low blood sugar levels. |
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Medications that can cause hypoglycaemia |
Insulin, Sulphonylureas (e.g. Gliclazide), Meglitinides (e.g. Repaglinide) |
Yes – regularly before, during, and after exercise |
These medications can lower blood sugar too much during physical activity, increasing the risk of hypoglycaemia. |
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Medications that do not typically cause hypoglycaemia |
Metformin, DPP-4 inhibitors (e.g. Sitagliptin), SGLT2 inhibitors (e.g. Dapagliflozin), GLP-1 receptor agonists (e.g. Semaglutide), Pioglitazone |
Yes – optional but useful |
Monitoring helps you understand how exercise affects your blood sugar. |
When should I monitor blood glucose?
Blood glucose should be checked at 3 time points.
Before exercise:
Two blood glucose readings should be taken at least 10 minutes apart before exercise so that the starting glucose is known as well as the direction in which the blood glucose is going.
During exercise:
If it’s possible, blood glucose should be checked every 30 minutes during exercise.
After exercise:
Blood glucose should be checked on finishing, an hour later and 6 hours later (or prior to bed). If you have done a new exercise or exercise for longer than 2 hours then blood glucose should be checked at 3 am.
Further resources
Type 1 diabetes: Type 1 Diabetes and Physical Activity online course
Type 2 diabetes: Exercise and Physical Activity: Healthy Living
