Your insulin dose may have to be reduced to match your level of activity. Although dosing needs will vary a lot depending on the intensity of each activity, the basic advice is:
• Reduce your dose of fast-acting insulin for the meal before physical exercise by 30% for moderate-intensity activity and by 50% for high-intensity activity.
• Reduce your insulin dose for the meal after exercising by 20-30%.
• Reduce your dose of slow-acting insulin by 10-20% the evening after exercising.
The reduction in your doses will depend on the intensity of your physical exercise, and in order to learn how exercise affects your body, you should take a blood glucose reading both before and after exercising. The dose reductions recommended above assume that the amount of food you consume remains constant. But since you are likely to have a bigger appetite after exercising, your dose reduction should then be smaller to match.
Physical activity can in itself:
• Acutely lower blood glucose
• Cause increased insulin sensitivity afterwards.
• Increase glycogen synthesis after excise, meaning that more glucose is converted into glycogen for storage in the muscles and liver. This effect may last several days, depending on the intensity and duration of the exercise.
If you have type 1 diabetes, this means you will have to try out dose reductions with great care initially by taking frequent blood glucose readings to avoid hypoglycaemia during and/or after exercising. Your insulin doses can often be reduced on the days you exercise.
Because increased insulin sensitivity may last for several days, it is also a good idea to take dextrose or another rapidly absorbed carbohydrate with you during this initial period.
Poor glycaemic control
If you have poor glycaemic control of type 1 diabetes, you may achieve a blood glucose reduction from moderate physical activity (slightly tiring activity). However, high-intensity exercise (i.e. very exhausting activity) increases your blood glucose for two reasons: glucose uptake in the body is reduced due to lack of insulin, while the hormones that stimulate production of glucose in the liver are released as normal.
Studies show that increased physical activity does not necessarily result in generally improved glycaemic control in type 1 diabetes, but there is no evidence that increased physical activity worsens glycaemic control. A number of elite athletes in both endurance and strength disciplines have type 1 diabetes.