Exercise and why blood glucose levels go up

Regular exercise is a great way to manage blood glucose levels and provides many other benefits to keep us healthy. Why do glucose levels sometimes rise during exercise?

Exercise can help insulin work better, lower blood pressure and cholesterol levels, reduce the risk of heart disease, decrease stress and also assists with maintaining a healthy weight.  The effect exercise has on your blood glucose levels, however, will depend on the type, intensity and duration of your chosen activity.  Other variables might also include timing of medication and meals eaten before exercise.

The general consensus is that exercise will lead to a reduction in blood glucose levels and help with long-term management.

High-intensity exercise can cause peaks

However, the short-term response can vary, particularly with high-intensity exercise such as running, interval exercise or resistance training.  With high-intensity exercise, there is an increase in your heart rate and the fast-paced movements cause the release of different hormones, including adrenaline.  This stimulates the release of glucose from places such as your liver to fuel this high intensity movement.

As a result, you may see a short-term (over minutes to hours) increase in your blood glucose levels, but the long-term outcome (over one to two days) will bring about a sustained decrease in blood glucose levels.  So, if you’ve ever experienced an increase in your blood glucose levels shortly after this type of exercise, don’t be alarmed, this is a normal response.

Alternatively, lower and moderate intensity exercise such as walking or swimming will lead to both a short-term and long-term reduction in your blood glucose levels, as this type of exercise utilises the excess glucose floating around in the bloodstream. This type of exercise is more sustainable for most people and forms part of the National Physical Activity Guidelines with the goal of 30 minutes of moderate intensity activity on most days of the week.

Become familiar with your BGLs and exercise

It’s important to become familiar with your blood glucose levels in response to exercise.

When starting a new exercise, it’s a good idea to check blood glucose levels before, during and after to see how your body reacts to different activities and to help with planning for future exercise sessions.  By understanding your response to exercise, you can avoid adverse events such as hypoglycaemia (lows) and hyperglycemia (highs).

If your blood glucose level before exercise is over 15mmol/L, and it is unexplained, check your blood ketone levels. Mild to moderate aerobic exercise can be started if ketones are less than 0.6mmol/L.  Intense exercise should be avoided, however, and it’s recommended that blood glucose levels are checked during and after exercise.

For more guidance with exercise, please see your doctor for a referral to an Accredited Exercise Physiologist.

By Hayley Nicholson
Diabetes Queensland Exercise Physiologist, CDE 

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