How does exercise impact blood sugar?

Different types of exercise impact your blood sugar in wildly different ways due to how your body fuels the activity. Aerobic exercise—like jogging, swimming, or cycling—is a steady-state activity. Your muscles require a continuous stream of energy, so they absorb glucose directly from your bloodstream, often without needing extra insulin. This causes a reliable drop in blood sugar, sometimes continuing for up to 24 hours post-workout. Conversely, anaerobic exercise—like heavy weightlifting, sprinting, or high-intensity interval training (HIIT)—is an intense, physical stressor. Your body reacts by releasing adrenaline and cortisol. These stress hormones signal your liver to dump massive amounts of stored glucose into your bloodstream to fuel a "fight or flight" response, causing an acute, temporary blood sugar spike. To manage this, test before, during, and after workouts. If you are doing cardio, you might need to lower your pre-workout insulin or eat a small carb snack beforehand. If you are lifting heavy, you might actually need a small correction dose of insulin. Combining both—lifting first, then doing cardio—can often keep your levels remarkably stable.