Adjusting Mealtime Insulin (rapid-acting, bolus)
Reduce the mealtime insulin dose before the exercise by 25% for mild intensity exercise to 75% for moderate intensity exercise.
Example: Say you were going to eat a meal which you would normally cover with 8 units of short-acting bolus insulin and then wanted to go cycling with friends for an hour, then cut your usual insulin dose to between 4 and 6 units (this will depend how energetic the cycling is!)
Remember to review this… the reduction in insulin may have been too much or not enough so you can change it the next time you exercise!
For this method you would use your own carbohydrate ratio to reduce the insulin by the right amount.
Using the ExCarbs theory of using up 1 gram of carbohydrate per kg weight for every hour of exercise (See ExCarbs) you can calculate how much to cut down your insulin.
If Jane, who weighs 60 kg wants to do an hour of an aerobics class 90 minutes after lunch we can assume she is going to use up 60 g of carbohydrate.
If her carbohydrate ratio is 1:10 (i.e she needs 1 unit of insulin for every 10 g carbohydrate) then she will need 6 units less of insulin with her meal. So if she has a meal of 75 g carbohydrate she would normally take 7.5 units but on this occasion she would only take 1.5 units (7.5-6 units).
Jane would then need to check her blood sugars and can adjust this change next time she exercises if she needs to!
John (72 kg) takes his dog for a walk 2 hours after dinner. He is going out for 30 minutes but walks quite hard up and down hills (moderate intensity).
We can assume he will use up 36 g of carbohydrate (1 hour would be 72 g so 30 minutes is 36 g). For his dinner he is having 80 g carbohydrate with a carbohydrate ratio of 1:8. Usually he would take 10 units of insulin for this meal but on this occasion he will take 5.5 units (10 units minus the 4.5 units for the exercise).
Again, if he does this regularly he can learn from previous blood glucose readings and adjust the doses if necessary.
If you are doing a specific exercise you can look up the ExCarbs from the table and use this in your calculation.
Sarah (68 kg) is going swimming 2 hours after breakfast. She will be swimming for 1 hour. According to the table she will use up 56 g of carbohydrate per hour.
For breakfast she has 80 g of carb with a carb ratio of 1:8 so she would normally take 10 units of insulin.
On this occasion she would take 3 units (10 units -7 units accounted for by exercise). (If her exercise would take up 56 g carbohydrate then she would only need to cover 80-56 g ie 24 g carbohydrate which is 3 units insulin).
That if on any of the occasions the exercise doesn’t happen for some reason that you will probably need to take a correction to bring the blood sugar down instead of the exercise!