Now that we have a good deal of experience with using automated insulin delivery systems in the management of diabetes, it has become clear that certain aspects of management are trickier than others. This is true whether you are using the Medtronic 670G system, the Tandem system with Control IQ, or even the DIY looping systems. Today I would like to highlight how we are learning to manage exercise, as many of the families with whom I work tell me that handling exercise remains a difficult challenge.
The first thing to understand is that exercise can have different effects on blood sugar:
1) Slow and steady exercise (aerobic) such as jogging, walking, biking or slow swimming may reduce blood sugar during the activity and for many hours afterwards. Prior to automated insulin delivery, many of you would often take a small exercise snack (uncovered with insulin) to avoid hypoglycemia, in addition to decreasing the basal insulin before and during as well as after the activity. The reality however is that it is very difficult to take exactly the right amount of carbohydrate to avoid mild hyperglycemia. This is critical in an automated insulin delivery system because once the system senses that sugar is rising, it will respond by giving extra insulin which can often lead to hypoglycemia, either during or after the activity. Certainly it is helpful to aim for a bit higher blood sugar by using a temporary target on the Medtronic system or the exercise feature on the Tandem system, but doing so is often not quite enough. The key is to understand that the system is not only looking at the current sugar but projecting where the sugar will be in the future. Therefore, the key is to avoid giving too much carbohydrate while the system is active to avoid the hyperglycemia that causes the system to give extra insulin in the first place. For example, small amounts of carbohydrate given every few minutes (like Gatorade) often work well. Finding out how much carbohydrate to give to keep the blood sugar in the low 100 range takes practice and effort. Your care team can make suggestions about how much carbohydrate would be suggested with given activities and taking into account your child's weight.
2) High-intensity exercise (anaerobic) often will cause the body to make lactate. This type of exercise (sprint swimming, sprinting events in track, wrestling matches as a few examples) can cause the blood glucose to rise very quickly. The automated insulin delivery system will often give a good deal of extra insulin causing significant hypoglycemia. We find that it is often wise to turn off or suspend the system during these events and resume it as the blood sugar comes back down toward normal.
Everyone's response to exercise is different. The most important thing is to learn from your experience and talk with your diabetes team if you need suggestions. Good luck, and have fun!