The insulin going into the body from a pump can take upto a few hours to actually start working so to use this method the basal rate needs to be reduced about 90 minutes before exercise starts. Also, the reduced basal rate should be continued throughout the exercise and until about 90 minutes after the end of exercise (this is to reduce the risk of hypoglycaemia after exercise).
How much to reduce the rate down by is a little more tricky and should be based on experience of previous exercise patterns!
The maximum reduction would be 50% as too little insulin in the body can be dangerous. Try starting with a 50% reduction but keeping a careful check on the blood sugar and then next time changing the percentage reduction.
Our aim at Excarbs.com is to help people with diabetes using insulin to feel comfortable with taking up exercise – our advice is not aimed at elite athletes but hopefully covers the basic rules for most people living with diabetes.
Remember that if exercise is sustained you will become much more sensitive to the effect of insulin and the dose needed will fall which is a really good result!