If you use a pump, you can set a temporary basal starting 30-60 minutes before you start exercising and run it until you finish. How much you decrease the percentage depends on the individual, so you will need to experiment a bit for your most common types and durations of exercise. Choose something simple and consistent to experiment with such as a 30-minute brisk walk, start with 50% and adjust from there. It’s still a bit hit or miss because exercise can also influence various hormonal fluctuations such as adrenaline and cortisol, either of which can goof up your BG. After exercise, many people need to run a different temporary basal rate (higher or lower) for the next 2-3 hours to cover the aftereffects, even longer if you went on a 1/2-day hike or something. If you are not using a pump, try a protein bar or nut bar before you exercise to give you a little carb and some protein to extend the effect, and of course bring some with you along with plenty of candy or glucose tabs. I would also highly recommend the book “Diabetic Athlete’s Handbook” by Sheri Colberg. It is helpful to understand the body’s reaction to exercise and manage any level of exercise, even dancing or yoga.