Plan ahead so that you have eaten and taken your premeal insulin 1-2 hours before you start exercising, otherwise you risk having the greatest blood glucose-lowering effect right at the beginning. If you are using a rapid-acting insulin it may be better to reduce the dose by 1-2 units if you are going to exercise within 1-2 hours of the injection.
Test your blood glucose before starting the exercise. If it is below 5-6 mmol/l (90-110 mg/dl) you should eat something before starting. If you have ketones in your blood or urine too, this is a sign that your cells are starving. You should wait until your blood glucose level has increased before you start your exercise.
If your blood glucose is above 15-16 mmol/l (270-290 mg/dl) you should check for ketones before starting the exercise. If your ketone levels are raised, you should not exercise until 1-2 hours after you have taken extra insulin (0.05-1 U/kg, 0.25-0.5 U/10 lb).
Eat something extra during exercise if the session lasts more than 30 minutes. Depending on your body size, a half to a whole banana (or other source of 10-20 g of glucose) is usually about right. Find out what suits you best. Take blood tests while you are exercising and note them in your logbook for future reference.
Eat a large meal after the exercise, preferably something with a high carbohydrate content, like sandwiches.
Decrease the insulin doses following exercise (evening premeal by 1-2 units and bedtime dose by 1-2, up to 4 units, or 10-20% decrease using temporary basal rate with a pump). If you exercise more than 3-4 times a week, the increased insulin sensitivity that your exercise causes will probably be effective “round the clock”. You will therefore be unlikely to need to lower your insulin doses as much in this situation since they will already be adjusted for it. For seasonal sports you may need to lower your insulin 24 hour dose considerably during active season, e.g. up to 40% when playing ice hockey.
If you exercise to lose weight, it is important to lower the premeal dose instead of eating more after exercising.
This content is based on Dr Ragnar Hanas' helpful book, Type 1 Diabetes in children, adolescents and young adults. Click here to order copies of Dr Hanas' book online.
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