PHYSICAL ACTIVITIES AND TYPE 1 DIABETES

Keeping up a physical activity schedule if you have Type 1 diabetes is an exciting challenge for your diabetes management skills. It helps if you start with a clear understanding of the interactions between insulin and physical activity.

 

KEY POINTS

  • Most people find physical activity improves their feelings of wellness and vitality. It also helps in managing stress.

  • Physical activity makes your body’s cells more sensitive to the action of insulin.

  • Your body remains more sensitive to insulin for up to 24 hours after physical activity. You may need to reduce your post physical activity insulin and / or eat more carbohydrates following physical activity.

  • The key to managing physical activity safely with Type 1 diabetes, is to monitor your blood glucose frequently and use this information to adjust your food and physical activity accordingly.

  • Avoid injecting pre-physical activity insulin into any area of working muscle (it may get absorbed much more quickly than usual if you do).

  • There are risks to physical activity. You should have a thorough medical check and consult with your diabetes specialist team before starting a physical activity routine.

To begin with it is useful to understand how a person without diabetes uses glucose during physical activity.

How the body manages its glucose levels during physical activity in people without diabetes

During physical activity, the muscles work harder and need more glucose to burn as energy. They pull glucose out of the bloodstream (blood glucose), as well as using up glucose that has been stored in the muscles (glycogen). Insulin works on the wall of the cell to allow glucose to get in.

During physical activity, the muscle cells become more sensitive to the action of insulin. This means that the body doesn’t need as much insulin to achieve the same job (moving either stored glucose or blood glucose into the muscle cells where it can get burned up). Because of this, the body starts to gradually reduce its production of insulin.

After about 30 minutes of moderate physical activity, the supply of glucose from the blood and from the stored glucose in muscles (glycogen) starts to run out. Blood glucose levels start to slightly drop. These slightly lowered blood glucose levels cause the body to change its hormone levels again. The hormone levels that it changes are insulin, glucagon and adrenaline. The body decreases the amount of insulin even further and increases the amount of glucagon and adrenaline.

The change in these hormone levels then causes the body to do two things:

  • To switch to using stored glucose from the liver

  • To stimulate the liver to start making new glucose from stores of protein and fat

The end result is that although existing blood glucose and stored glucose (glycogen) in the muscles are used up, the body maintains a constant blood glucose level. This is because the body has changed its hormone levels and by doing this has turned the liver into a glucose factory. The liver releases its stored, or newly made glucose, into the bloodstream.

People who are able to make these hormone level changes automatically can conduct physical activity over prolonged periods (eg. running a marathon) without any dramatic change in their blood glucose levels.

How the body uses glucose during physical activity if you have Type 1 diabetes

When you have Type 1 diabetes, your body cannot manufacture its own insulin. Therefore, your body cannot (by itself) make the changes to insulin levels that are needed to keep your blood glucose level constant during physical activity.

Many people with Type 1 diabetes also have difficulty in adjusting the level of glucagon (another hormone) in their bodies. This is particularly so if they have had Type 1 diabetes for more than 5-8 years. Glucagon is a hormone your body makes to help bring your blood glucose level back up when it is low.

So, when you have Type 1 diabetes, your glucose use during physical activity is quite different from people who don’t have Type 1. Your body does not have the ability to maintain your blood glucose levels at a constant rate automatically.

These factors influence what happens to your blood glucose levels during physical activity:

  • What your blood glucose is before and during physical activity

  • How much injected insulin you have on board and when it is peaking

  • How much and what type of carbohydrate food you have before and during physical activity

  • The duration and intensity of your physical activity

  • The level of circulating insulin will depend on the timing of your last insulin injection and the type of insulin used

Tips for exercising safely if you have Type 1 diabetes

If you are starting a physical activity or sporting programme and you are new to managing your diabetes during physical activity, get help from your diabetes nurse educator or diabetes specialist before you start. Your diabetes team can help you plan how you adjust your insulin doses and food intake for physical activity.

If you have any complications of diabetes, including heart disease, retinopathy, neuropathy or kidney problems, see your diabetes team before planning a physical activity routine. Some forms of physical activity are safer than others when you have complications.

When you are starting out with a physical activity routine, start small and build up your fitness gradually. If you have been doing no physical activity, start with 5-10 minutes of moderate physical activity daily (like brisk walking), and build this up by 5 minutes every 3-4 days until you are doing 30 minutes daily. Always conduct physical activity within your comfort zone. If you are out of breath its best to slow down until you are comfortable again.

MANAGING YOUR BLOOD GLUCOSE DURING PHYSICAL ACTIVITY

It is often not a safe choice to conduct physical activity at a time of day when your short-acting insulin is peaking. This is because physical activity makes you more sensitive to insulin. You are more likely to have a low blood glucose during physical activity when your short acting insulin is peaking.

The best times to conduct physical activity are often:

  • First thing in the morning before your breakfast short-acting insulin peak (but after a small carbohydrate snack – about 15-30 grams depending on the duration and intensity of physical activity planned), or

  • At the tail end of your breakfast short-acting insulin peak (before lunch but after a mid morning snack), or

  • At the tail end of your lunchtime short-acting insulin peak (before evening meal but after a mid afternoon snack).

It is best to get advice from your diabetes team on your own specific insulin action times when planning physical activity. If you have to conduct physical activity at a time when your short acting insulin is peaking (eg. for a scheduled sports game), it pays to significantly reduce your pre-physical activity dose of insulin. Avoid injecting any pre-physical activity insulin into an area of working muscle.

Pre-physical activity blood glucose check?

Check your blood glucose before your physical activity. If you are organised enough, it is a good idea to test your blood glucose twice before physical activity. Test 30 minutes before and again just before you begin. This way you will know whether your blood glucose level is stable or dropping. If it is dropping, you may need an extra carbohydrate snack before starting.

Pre-physical activity snack?

Your pre-physical activity blood glucose level will tell you if you need a snack before starting. The following chart provides a starting point only for how many grams of carbohydrate you may need. You will need to test and record your own blood glucose during and after physical activity to see if these quantities seem right for you.

Please note: CHO is shorthand for carbohydrate