Exercise is important in the management of type 1 diabetes. There are some factors that have to be acknowledged to keep you safe and exercising at your most effective level. This article discusses those considerations.

Reduction in BGLs

In both the short and long term, exercise reduces blood glucose levels (BGLs).

Both insulin sensitivity and glucose uptake can be significantly increased for up to 48 hours after exercise. That’s a big benefit from a single bout of exercise. Adding this to the many other benefits that exercise can also induce means exercise should be a staple in type 1 diabetes management.

Safe and effective exercise

However, exercise while living with type 1 diabetes can pose some considerations that need to be acknowledged in order to ensure it is completed safely and effectively.

This article discusses:

• the effect of exercise on your BGLs
• the considerations behind blood glucose monitoring and exercise
• how to prevent lows during and after exercise
• and where you can find further information on type 1 diabetes management

Insulin works more effectively

Exercise results in a host of benefits including increased insulin sensitivity and an overall increase in glucose uptake through insulin-dependent and non-insulin dependent pathways. This means your insulin is working more effectively and your muscles don’t need insulin to take up some of this glucose.

While this is one of the greatest benefits of exercise, it’s important to note that this increased glucose uptake and insulin sensitivity means your body will be absorbing more glucose than you may be used to.

Hypoglycaemic risk

As such, you may experience larger decreases in your blood glucose readings than normal. This can leave you at a greater risk of a hypoglycaemic event, or very low blood glucose levels.

For example, if you were to administer your regular insulin dosage and experience a decrease in your BGLs, the same insulin dosage may show a greater effect after exercise. Therefore, it’s important to consider your insulin dosage and the timing of your medication when exercising.

Increase carbohydrate

If you’re considering adjusting your insulin dosage or timing around your exercise, it’s best to consult with your GP, Diabetes Educator, or Endocrinologist.

You may also decide to increase your carbohydrate intake both before and after your exercise session to prevent your BGLs from dropping too low. If you’re considering any major changes in your eating habits, consult with an Accredited Practising Dietitian.

Now that we know that your blood glucose uptake will improve with exercise and the potential risk of hypoglycaemia, we can discuss the recommendations around BGLs before starting exercise.

Aerobic reduces BGLs

Before we discuss safe ranges to exercise, we must first consider the impact of exercise on your BGLs based on the type of exercise.

Aerobic (or cardio) exercise, which is generally lower in intensity and longer in duration, can reduce your BGLs in the short term (immediately) and in the long term (48 hours’ post-exercise).

This is because your muscles will draw from the glucose in the blood for energy.

Resistance training can increase BGLs

Resistance exercise (weights) or high intensity aerobic exercise (HIIT, sprints) may result in a short term increase in your blood glucose.

This is due to the release of hormones such as cortisol or adrenaline that stimulate the release of glucose into the blood stream to supply the demand for energy.

Safe BGL range

Considering this information, a safe blood glucose range to start exercise when living with type 1 diabetes is between 7.0-10mmol/L. This allows a buffer between a possible hypo (<4.0mmol/L) when considering the impact of insulin.

Consuming carbohydrates prior to exercise can help ensure your levels do not reach this point.

Adjust your exercise according to your BGL

If your blood glucose is higher than 10.0mmol/L, you may wish to consider the type of exercise you complete and remove the need for carbohydrates prior to exercise, along with completing lower intensity endurance-based exercise.

If your blood glucose is a bit low or you’ve recently administered your insulin, you may choose a resistance-based or higher intensity exercise.

Check for ketones

Another important consideration is the presence of ketones in the blood. If you are experiencing blood glucose readings higher than 15mmol/L, check your blood for ketones. If you’re feeling well and your ketones are below 1.5mmol/L it’s safe to start  light aerobic exercise only with consistent monitoring of blood glucose throughout the exercise session.

If they are above 1.5mmol/L, it is not safe to exercise.

Prevent hypos

Now that you know whether or not you’re safe to start exercise, we need to be prepared to prevent significant decreases in blood glucose readings during exercise that may result in a hypoglycaemic event.

Your first step is to monitor your blood glucose not only before, but during and after exercise.

You may choose a mid-way point, or potentially more frequently as you learn about how your body and blood glucose responds to exercise. This will leave you equipped to take action if necessary.

Two carb exchanges

Your next step is to ensure you always have appropriate food and/or drink available in case your blood glucose begins to drop. It’s always recommended that you keep at least 1-2 Carbohydrate Exchanges (15g carbohydrates) of both fast-acting (high GI) and slow-acting (low GI) carbs.

Some examples of fast-acting carbohydrates include 5 to 6 jelly beans, glucose tablets, and half a can of soft-drink or fruit juice. Examples of slow-acting carbohydrates include a piece of fruit or a slice of bread.

When to stop

If you notice your blood glucose begins to drop below 7mmol/L then stop exercising, consume 1-2 exchanges of your fast-acting carbohydrate, and re-test after 5 minutes.

If your levels return to normal, consume 1-2 exchanges of your slow-acting carbohydrate, re-test, and if safe you can resume exercise. If your BGLs drop below 4mmol/L (hypoglycaemia) then action the above but exercise cannot be resumed.

Low BGLs after exercise

Finally, it’s important to consider the residual effect exercise will have on your insulin sensitivity and glucose uptake. You may experience more significant reductions in BGLs hours or even days after exercise.

As such, you may wish to consider adjusting your insulin dosage or increasing your overall carbohydrate intake to prevent the risk of post-exercise hypoglycaemia. Discuss this with your health care team.

OzDAFNE info

Managing type 1 diabetes can be a challenging and time-consuming task. For more information on any of this content, visit the NDSS website at www.ndss.com.au. You can also call the NDSS Helpline on 1800 637 700 to speak with an Accredited Exercise Physiologist, Accredited Practising Dietitian, Credentialed Diabetes Educator, or a Psychologist.

Check out the OzDAFNE Program for further information on how to live well with type 1 diabetes, including information on counting carbohydrates and adjusting insulin dosages, plus more information on exercise and managing hypoglycaemia.

Jonathon Fermanis
Accredited Exercise Physiologist