Regular physical activity, including structured exercise, is one of the main pillars in effective diabetes management. It can be a real game changer due to its effectiveness in reducing blood glucose levels (BGLs) both during and for a period of up to 24 hours afterwards. It is the un-swallowed pill that you can take every day to help you manage your levels; a form of natural medicine! Staying active on a regular basis will not only mean less frequent highs (known as hyperglycaemia), but it will also reduce the risk of diabetes related complications in the future.

Understanding how our bodies respond to exercise is one of first important steps we should make when undertaking a new regimen. In the case of diabetes, it is vital to understand how BGLs respond to different activities. The way your body responds can differ largely depending on what medications you are taking, your current fitness level, how long you have had diabetes and characteristics of the exercise you are performing (type, duration, intensity). Due to the blood glucose lowering effects of exercise, the recommendations generally emphasise the importance of ensuring BGLs are greater than 6mmol/L prior to undertaking any exercise.

For this reason understanding when BGLs are too low to commence exercise safely is important, but it also raises the question –  can BGLs be too high to exercise? The short answer to this question is yes!

How high is too high?

The general BGL guidelines for hyperglycaemia and exercise are:

Type 1 diabetes:

• Safe to exercise: between 6-15mmol/L
• Exercise with caution: >15mmol/L, no ketones present and feeling well
• Delay exercise: >15mmol/L with ketones present

Type 2 diabetes:

• Safe to exercise: between 6-15mmol/L
• Exercise with caution: >15mmol/L and feeling well
• Delay exercise: >15mmol/L and feeling unwell

These recommendations are in place because if BGLs are high prior to exercise, there is potential for exercise to make them go even higher. For more personal guideline please discuss with your healthcare team.

Exercise-induced hyperglycaemia

Certain forms of exercise have the potential to cause an increase in BGLs in the short term, this is known as exercise-induced hyperglycaemia. This includes exercises that are high in intensity such as sprinting, jumping and moderate to heavy resistance training. This is mainly due to the effect this form of activity has on the production of counter regulatory hormones such as adrenaline. Basically, the body sees intense exercise as a type of stressor and there is a subsequent release of stress hormones which signals the body to increase glucose production and block insulin action. It may be a sign that you are pushing yourself too hard or your body is under a significant amount of stress.

This effect is generally temporary with levels returning to pre-exercise levels or lower in the 1-3hrs following exercise cessation. For those with type 1 diabetes, some insulin may be required to assist with bringing BGLs down depending on the reading.  This is a normal response to this type of activity and should only cause concern if BGLs remain elevated for long periods after the activity ceases.

Tips for reducing the risk of exercise-induced hyperglycaemia:

• Don’t exercise with ketones present – exercise will likely elevate BGLs further when the body is in this state (leading to Ketoacidosis). This is more likely to occur with type 1 diabetes, however people with type 2 diabetes should still be aware.
• Avoid vigorous activities if BGLs are high – if levels are high but ketones are negative, consider modifying exercise program to make it a light or moderate intensity session. Activities such as walking, cycling on a stationary bike or level ground, light aerobics will generally lead to a reduction in BGLs.
• Sick days and hydration – avoid exercise when you are feeling unwell as BGLs will likely be elevated during this time. Adequate hydration is vital when you are sick to prevent dehydration.