Physical activity & 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.

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 causes the body change some 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 it's 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.

Three main 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 (eg: 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 if you 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 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.

Type of exercise	Pre-exercise blood glucose level less than 6mmol	Pre-exercise blood glucose level of 6 - 10 mmol	Pre-exercise blood glucose level of 10 -15mmol
Short duration (20-30 mins) of low-moderate intensity e.g., walking	25g CHO	0g CHO	0g CHO
Short duration high intensity (e.g., running, squash)	25g CHO	0g CHO	0g CHO
Moderate duration (45 - 60 mins) moderate intensity e.g., cycling,swimming	25 - 50g CHO	0 - 25g CHO	0g CHO
Long duration (60-75 mins) moderate intensity e.g., triathlon, soccer,football, jogging	50g CHO	25 - 50g CHO	25g CHO

Note: CHO is shorthand for carbohydrate.

Blood glucose higher than 15mmol/L?

If your pre-physical activity blood glucose is greater than 15mmol/L you should check your urine for ketones. If no ketones are present and your blood glucose has been falling it is safe to physical activity moderately – so long as you check your blood glucose often and stop physical activity if your blood glucose is climbing. If ketones are present it is best to rest, treat the blood glucose with short-acting insulin, drink plenty of low calorie fluids and delay physical activity for the day.

Carbohydrate during physical activity?

It pays to check your blood glucose about every 30 minutes when you are exercising. Most people seem to need about 50 - 60 grams of carbohydrate per hour during physical activity. This is often easiest taken as fruit juice, dried fruit, sports drink or as a dextrose gel pack (available at many sports shops).

Monitor, monitor, monitor . . .

Your best guide to managing your blood glucose levels during and after physical activity is to monitor your blood glucose levels frequently - before, during and after physical activity. Keep a record of these along with how much you eat before and during physical activity. Also record the intensity and duration of the physical activity. Over time you will come to understand your body's usual response to physical activity.

It is more important to test your blood glucose level if you are trying a new form of physical activity. This will tell you how your blood glucose levels are responding to it. If you keep a record of your responses to different physical activity this will help you over time.

Fluids

It is very important for all people to keep their fluid intake up during physical activity, but especially so for those with diabetes. When your blood glucose levels are even a little higher than the normal range you are much more prone to dehydration. If you do get dehydrated this can worsen high blood glucose levels.

Am I more prone to low blood glucose levels following physical activity?

Yes. Your body can remain much more sensitive to insulin for up to 24 hours following physical activity. Also during physical activity your body uses up its stores of glucose (from muscle and liver). For the next 10 -24 hours your body will be replacing these stores and taking the extra glucose from your bloodstream.

For both these reasons you are much more prone to low blood glucose levels following physical activity. It pays to reduce the dose of insulin you take following physical activity. Your diabetes team can give you some pointers as to how much to reduce by. You may also need to take extra carbohydrate.

If you plan physical activity later in the day you will need extra carbohydrate at dinnertime. It is also wise to consider reducing your overnight insulin.

Over time, as you get established into a regular physical activity routine, you may find that your insulin doses throughout the day will need reducing. If you are getting frequent low blood glucose levels, or if you feel you are having to eat more food than you would like just to keep your blood glucose levels up, get help from your diabetes team to help you work out the best reductions to your dosages.

Safety issues

Because you are much more prone to having low blood glucose levels during or after physical activity, always carry some short acting and some long acting carbohydrate with you. Carry some form of identification on you that shows that you have diabetes and are on insulin. It is often best to plan physical activity with another person. If you are exercising on your own let someone know when you are expected back.

Remember to take special care of your feet when exercising. Your choice of shoes for physical activity is very important. If you are unsure as to what to buy consult a specialist shoe store or a podiatrist. Make sure you try your shoes on at the end of the day (when every ones feet are a little more swollen than first thing in the day). And also when you are wearing thick sports socks. The socks you choose should be seamless if possible. Shock absorbers fitted to your shoe are a plus.

Check your feet daily after physical activity. If you notice any problems get help quickly. If you have any established foot problems it is best to plan a form of physical activity that does not expose your feet to high impact, eg: cycling or swimming. See our section Diabetes and Your Feet (link to diabetes and your feet page) or more information on caring for your feet.