Physical Activity and Exercise: Blood Glucose and Complications

This page discusses what you need to know about how physical activity and exercise as someone with diabetes.

 

 Content

Impact of Intensity of Exercise on Blood Glucose 

Exercise intensity refers to how much energy (calories) is used by the body when exercising.

Depending on intensity, different types of activities can have a varying impact on blood glucose levels. This depends on which energy system the body uses during the exercise, although in reality a lot of types of exercise involve both.

Lower intensity exercise uses a larger percentage of energy from fat, as the body does not need to quickly and efficiently produce energy to maintain the activity. When walking a mile, 20% of fuel will be supplied via glucose and 80% from fat. Higher intensity exercise obtains a larger percentage of energy from carbohydrates, as the body is able to produce this quickly, making glucose the main source of energy in such activities.  When running a mile at a strenuous pace, as much as 80% will come from glucose.

The higher the intensity, the greater the impact on blood glucose level

Strategies to Measure Intensity 

There are several ways to measure exercise intensity. 

Talk Test

This is a very easy test to help you figure out your exercise intensity. Just pay attention to how breathless you are. In general, if you're doing moderate-intensity activity you can talk, but not sing, during the exercise. If you're doing vigorous-intensity exercise, you will not be able to say more than a few words without pausing for a breath. 

Rate of Perceived Exertion

The Borg Rating of Perceived Exertion is another way of measuring physical activity intensity level. Rate of Perceived Exertion is how hard you feel like your body is working. It is based on the physical sensations you experience during exercise, including increased heart rate, increased respiration or breathing rate, increased sweating, and muscle fatigue.

Try to appraise your feeling of exertion as honestly as possible. Don’t underestimate it, but don’t overestimate it either. It’s your own feeling of effort and exertion that’s important, not how it compares to others. What other people think is not important either. Look at the scale below and the expressions and then give a number.                                                  

Borg Scale                  What Do The Numbers Mean?

6

no exertion at all

 

7

able to maintain pace

 

8

 

 

9

very light

9 corresponds to ‘very light’; like walking at own pace for some minutes in a healthy individual, feels comfortable but breathing is a little harder

10

 

 

11

 

12

 

 

13

somewhat hard

 13 on the scale is ‘somewhat hard’ exercise, but healthy individual still feels ok to continue, feels slightly breathless but can still talk.

14

 

 

15

hard (heavy)

 

16

 

 

17

very hard

 17 is ‘very strenuous’, a healthy individual can still continue, but has to push themselves, it feels very hard, able to keep fast pace for short time.

18

 

 

19

extremely hard

 

20

maximal exertion

 20 on the scale is ‘extremely strenuous’ exercise, for most people this is the most strenuous exercise they have ever experienced. STOP.

The optimal training target zone for a healthy adult is 12 – 16 on the scale.

Blood Glucose Monitoring 

If you are treated by insulin, you may find that exercise could lead to the development of either high blood glucose (hyperglycaemia) or low blood glucose (hypoglycaemia). It is important you become familiar with how different types of activity affect your blood glucose levels.

To help with this, if you have Type 1 diabetes you should frequently check your blood glucose levels:

  • Before exercise session
  • During exercise session (every 30 minutes)
  • After exercise session 

Frequent blood glucose testing allows you to identify when changes to insulin doses or food are necessary. This means that you can help prevent your blood glucose from going too high or too low.

Any changes to diabetes medications should be gradual, after thorough assessment of blood glucose readings and following discussion with your diabetes team. 

Blood Glucose Targets 

The following guidelines have been developed for those with diabetes who are treated with insulin.

If you have a starting blood glucose of less than 7 mmols / litre:

  • Eat 10 – 15 g of carbohydrate and recheck blood glucose after 10 minutes
  • It may be necessary to repeat this process until blood glucose greater than 7
  • If you have a low blood glucose (hypoglycaemia) prior to exercise, it may be best to postpone the activity for that day

If you have a blood glucose between 7 – 12 mmols / litre:

  • Go off and enjoy exercise 

If you have a blood glucose of greater than 12 mmols / litre:

For people with Type 1 Diabetes:

  • check for ketones, if present do not exercise and treat as per instructions outlined in the management of sick day rules
  • If no ketones present, it is ok to exercise but any additional carbohydrate should not be eaten until blood glucose has dropped below 12 mmols / litre

For people with Type 2 Diabetes:

  • Proceed to exercise, it is unlikely that additional carbohydrate will be required

Low Blood Glucose (Hypoglycaemia) 

During activity, the body needs additional oxygen and energy. The main source of energy comes from glucose, which is initially released from stores within the body’s cells, but as the exercise continues is taken from the blood and eventually the liver.

Exercise related low blood glucose (hypoglycaemia) is common in those with Type 1 Diabetes and, to a lesser extent, people with  Type 2 Diabetes using insulin or tablets which promote insulin secretion e.g. Gliclazide. Episodes of hypoglycaemia can develop during or after the exercise, in some cases as long as 24 hours later.

It is always best to plan ahead and where possible reduce your insulin dose, increase your carbohydrate intake, or in some situations to do both. Where you are unable to plan ahead, you will only have the option of eating additional carbohydrate.

When planning, it is important to consider your reason for exercise. If you are planning to lose weight, it would be best to reduce your insulin dose in advance.

Listed below are factors to consider prior to exercise to help prevent hypoglycaemia include:

  • Your reason for exercise
  • Duration and intensity of exercise
  • Impact of exercise on blood glucose by monitoring (before, during and after)
  • Time of day
  • Consider the timing and duration of action of any recent insulin
  • Injection site of recent insulin
  • Previous episodes of hypoglycaemia (within past 24 hours)
  • Always have treatment for low blood glucose (hypoglycaemia) on person

Prior to making any adjustments to your insulin regimen, it is important to develop an exercise management plan which should be constructed with the help of your diabetes team.

High Blood Glucose (Hyperglycaemia) 

Often the biggest concern for people with diabetes, who participate in regular exercise, is the development of low blood glucose (hypoglycaemia). This fear can lead to the consumption of additional carbohydrate, which is not required and can result in high blood glucose (hyperglycaemia) following exercise. Remember, you are only at risk of exercise related hypoglycaemia if you treat your diabetes with insulin or tablets which increase insulin production e.g. Gliclazide. In those situations, frequent checking of exercise before, during and after exercise will alert you to the need for additional carbohydrate. Consider, extra calories will also be consumed when unnecessary carbohydrate is eaten. This is an important consideration if you are exercising to lose weight. The fear of hypoglycaemia may also lead to unnecessary and inappropriate adjustments to insulin prior and post exercise, which may also lead to the development of hyperglycaemia

In those with Type 1 Diabetes, high blood glucose prior to exercise may lead to an even higher reading after the event. High blood glucose indicates that there is an inadequate supply of circulating insulin. Remember that insulin is essential for the body to transport glucose (fuel) to the exercising muscle. This can trigger the liver to release glucose from its stores, which can lead to higher blood glucose after the exercise. When insulin is lacking, the body will access other fuel sources, namely fat. A by product of this process is the production of ketones, which if left untreated could result in the development of DKA. As a consequence, it is essential to check for ketones when blood glucose is > 12 mmol. If ketones are present, exercise must be postponed and until this situation has been resolved.

A further factor which can result in a rise in blood glucose during exercise in those treated, is the type of activity being undertaken. Short, sharp activities which are high in intensity e.g. sprinting and weight lifting, increase the production of stress hormones such as; adrenaline and cortisol. These are often referred to as glucose raising hormones, due to the impact on blood glucose readings.

The responses noted above are most common in those with Type 1 Diabetes, but individuals with Type 2 Diabetes may also experience an increase in blood glucose following such events, particularly if they use insulin and administer too little for meals prior to exercise.

If you notice that your blood glucose readings rising during exercise, contact your diabetes team who will be able to help you manage the situation.

Exercising with Diabetes Complications 

The table below gives you information about exercising safely with specific diabetes complications. 

Table 1: Exercising With Diabetes Complications

Complication

Caution Activities

Promoted Activities

Heart Disease

Very strenuous activity; heavy lifting or straining; exercise in extreme heat or cold

Moderate activity such as walking; daily household tasks

High Blood Pressure

Very strenuous activity; heavy lifting or straining

Moderate activity such as walking; daily household tasks; keep hydrated

Peripheral Neuropathy

High impact, strenuous or prolonged weight bearing activities such as walking a long distance, running on a treadmill, step aerobics; exercise in extreme heat or cold; weight bearing exercise when you have a foot injury, open sore or ulcer

 

 

Light to moderate daily activities; exercise in a moderate climate; moderate weight bearing activities that are low impact such as walking, swimming, cycling, chair exercises

 

Those with peripheral neuropathy need to have appropriate footwear and should check their feet every day

Autonomic Neuropathy

Exercise in extreme heat; activities requiring rapid changes in movement

Mild to moderate aerobic activities and strength training, but increase the exercise slowly; keep hydrated

Retinopathy

Strenuous exercise, activities that require heavy lifting and straining; high impact activities; head down activities

Moderate activities that are low impact such as walking, cycling); moderate daily tasks that do not require heavy lifting, straining or the head to be lower than the waist

Peripheral Vascular Disease

High impact activities

Moderate walking (may do intermittent exercise with periods of walking followed by periods of rest); non weight bearing exercise such as swimming, cycling

If you have any complications associated to diabetes, you must always discuss any new activity with your diabetes team before you start.

Useful Resources 

The following websites have been specifically designed for those who have Type 1 Diabetes and participate in planned exercise on a regular basis:

 

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