Managing diabetes and exercise using multiple daily
injections (MDI)
Being active is an important part of a healthy lifestyle. Being more active can make blood glucose
levels harder to manage at times. This information sheet will help you to understand how to keep
your blood glucose levels stable during exercise.
About exercise and diabetes
You need to know a bit about different kinds of exercise to help you keep your blood glucose levels
stable. Your blood glucose levels can be affected by;
 Different types of exercise (aerobic or anaerobic)
 The amount of insulin in your body,
 How long your exercise or activity lasts. Exercise that lasts longer than 1 hour
will normally have more of blood glucose lowering effect.
The only way to know what happens to your blood glucose levels is to check before, during and
after activity.
before
exercise
during
exercise
after
exercise
twice in the hour before you
start
Are you steady, rising or
falling?
at the beginning and then every
30minutes if you can
Are you steady rising or falling?
as you finish then 1-2hourly
for a couple of hours, before
bed and between midnight
and 3am
Exercise can lower blood glucose levels for up to 24 hours. You may be more sensitive to your
insulin and need to reduce long acting insulin doses and reduced doses of insulin with food after
exercise.
Checking blood glucose levels is the only way to learn what happens during exercise
Insulin and exercise
The levels of insulin in the body affect how our blood glucose levels change with exercise. We have
a store of fuel (glycogen) in our muscles and liver that can be used for energy at the beginning of
exercise. The stores usually last about 45 minutes. If insulin levels are high (for example just after a
meal bolus) the liver cannot produce glucose for the muscles to use and blood glucose can drop
rapidly.
Remember
You need just enough insulin during exercise to allow your liver to produce the right amount of
glucose for your working muscles.
Caution
Low insulin levels allow the liver to release too much glucose and ketones may appear. If you have
ketones and a high blood glucose level you need to treat this before you exercise.
How do different types of exercise affect blood glucose levels?
Aerobic
exercise
Examples- running,
cycling, distance
swimming
usually lowers the
blood glucose levels
Anaerobic or
high intensity
exercise
Examples - sprinting,
weight training,
sports with lots of
short,sharp, fast
movements
May push blood
glucose levels up
during the exercise
Mixed
exercise
Examples - team
sports football,
rugby, hockey
Often blood glucose
levels will be more
stable
Aerobic exercise (which uses oxygen) will usually lower your blood glucose during and after
exercise, examples include running, swimming, cycling
if your exercise lasts longer than 30 minutes you will probably need to reduce your
insulin and/or have extra fast acting carbohydrate
for exercise that lasts for less than 30 minutes you may not need to lower your
insulin but you may need a little extra carbohydrate
Anaerobic exercise (does not need oxygen) may make your blood glucose rise during the
exercise and fall after the exercise, this is because you make more adrenaline during this
type of activity. Anaerobic sports are usually short, sharp & fast or strength and power
sports. Examples include, sprinting, basketball, weight lifting.
Some sports will be a mixture of aerobic and anaerobic exercise, e.g. football and team
sports. Mixed exercise may produce steady blood glucose levels.
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Exercise Snacks (Ex-Carbs)
You should aim to keep your blood glucose level around 6-8mmol/L before and during exercise, you
can adjust your basal and bolus insulin to do this or you can have extra carbohydrate. If you do not
adjust your insulin you will need more carbohydrate during exercise.
The amount of carbohydrate you need depends on
 The insulin adjustment you made 1-2hours before exercise
 The blood glucose level 10-15minutes before exercise
 The amount of insulin on board/active insulin
 How hard the exercise/activity is
 How long the activity lasts for
Exercise snack suggestions
Fruit/Diluted fruit juice
If your blood glucose level is below 5.5mmol/L before
Dried fruit
the start of any exercise you should have 15-20g low fat
Low fat cereal bars
carbohydrate to bring it above 5.5mmol/L.
Jelly sweets
If your BGL is below 8mmol/L at the beginning of your
Jaffa Cakes
exercise you will probably need to start having your
Sports drinks
exercise snacks at the start of the activity.
As a starting guide have 10-15g carbohydrate for every 30minutes of activity and adjust this
according to your BG levels.
Food after exercise
Eat a snack before bed whenever you have done 60 minutes or more exercise in the afternoon or
evening. This helps to maintain blood glucose levels overnight. A mixture of carbohydrate and
protein helps your muscles and liver to replace their glycogen stores. Examples of good bed time
snacks include milk shake and fruit, cereal and milk, crumpets with peanut butter.
Fluid and exercise
It is important when you are being active that you have plenty to drink. If
your blood glucose levels are high during exercise you will need to drink
more to stay hydrated.
Drink 2-300ml water or dilute sugar free squash, in the hour
before any exercise.
Try and drink during your exercise as well, about 100ml every 1015minutes.
Water is the best thing to drink during exercise that lasts for up to
60-90minutes. You can use sports drinks if you need extra
carbohydrate – drink some water as well
If you are exercising for longer than 60 -90minutes then a sports
drink can be useful to help you get the fluid you need and the
extra carbohydrate as well.
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Adjusting your insulin
You should aim to keep your blood glucose level around 6-8mmol/L immediately before and during
exercise you can adjust both the long acting background (basal) and fast acting food (bolus) insulin
to do this.
Fast acting meal time insulin (bolus insulin)
If you eat 1-2 hours before exercise then you can make a reduction in your mealtime fast acting
insulin dose to help prevent low blood glucose levels during sport and then make a similar
reduction with food eaten after exercise to prevent low blood glucose levels after exercise.
Lower your insulin by 25-75% if you give an injection with a meal 1-2 hours before exercise.
If your exercise is more than 2 hours after a meal and insulin injection bolus you may not
need to make any reductions
Meal time insulin should be injected before eating before exercise, also try and use the same
injection area for regular exercise. For example if you have a regular training session after an
evening meal always give your insulin in the same area for the meal before exercise on that day.
You should also think about avoiding injection sites that are near the active muscles e.g. avoiding
your legs if you are running.
Background insulin
Your long acting background insulin may also need to be adjusted to help prevent low blood
glucose levels after exercise.
You may find this easier if you have 2 injections of long acting insulin a day, one in the evening and
one in the morning. This will mean you can adjust your day time and night background insulin levels
separately.
Long acting insulin doses will need to be reduced
 when you are going to be active all day,
 when your activity is strenuous and
 If you will be exercising again the next day.
Background insulin may need to be reduced by 25-50%.
Active Insulin
If you use a smart blood glucose meter with a bolus wizard/advisor you can check how much active
insulin is present before you do any exercise. If your blood glucose level is ok and you have active
insulin you should take some extra carbohydrate before you start. Reverse your insulin to carb
ratio; if your ratio is 1unit to 10g carbohydrate take an extra 10g fast acting carbs at the beginning
of the exercise for every unit of active insulin.
Blood glucose targets for exercise
Before exercise above
5.5mmol/L
During exercise 6-8mmol/L
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Blood
glucose
<
5.5mmol
Aerobic exercise
Anaerobic exercise
Bring blood glucose back to normal, have a
15-20g snack before starting exercise. If you
have taken fast acting insulin in the 2 hours
before your activity have extra carbohydrate
1g/kg body weight per hour of exercise
Bring blood glucose back to normal,
have a 15-20g snack before starting
exercise. If you have taken fast acting
insulin in the 2 hours before your activity
have extra carbohydrate 0.5- 1g/kg
body weight per hour of exercise
5.5 Have exercise snacks, 10- 15g for each
Consider exercise snack if exercise lasts
8mmol
30minutes of activity. Increase the amount
longer than 30minutes. Increase the
of carbohydrate if you have ‘active insulin’
amount of carbohydrate if you have
‘active insulin’
8–
If no active insulin and exercise 30minutes or If no active insulin and exercise
11mmol/l less no snacks should be needed.
30minutes or less no snacks should be
If exercise lasts longer than 30-45minutes
needed.
and/or active insulin then exercise snacks will If exercise lasts longer than 30be needed.
45minutes and/or active insulin then
exercise snacks may be needed.
11 Between 11 and 14mmol/L you may not need Between 11 and 14mmol/L you may not
14mmol/L a correction dose if you have active insulin.
need a correction dose if you have active
You may need insulin with exercise snacks for insulin.
performance.
Beware Anaerobic exercise high blood
Drink plenty of fluids to prevent dehydration glucose may raise blood glucose levels.
Cover exercise snacks with insulin.
Drink plenty of fluids to prevent
dehydration.
14mmol/L Check for ketones and correct* blood
Check for ketones and correct* blood
or more
glucose.
glucose.
Drink plenty of fluids to prevent dehydration Anaerobic exercise with high blood
glucose may raise blood glucose levels.
Cover exercise snacks with insulin.
Drink plenty of fluids to prevent
dehydration.
*use only a half correction dose during exercise; do not exercise with a high blood glucose level and
ketones
You will learn through experience how different types of exercise affect your blood glucose
levels.
Your blood glucose responses to exercise and competition will change with time and your
fitness level – keep checking to stay in control and perform at your best
This information has been produced for use by diabetes healthcare professionals by
Francesca Annan, BSc, MSc, RD
Paediatric Diabetes Dietitian, Alder Hey Children’s NHS Foundation Trust
Produced September 2015 Review Date January 2016
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