Exercise — especially long, hard workouts — can lower your blood glucose for hours after you've stopped. This happens because workouts draw on your body's supply of glucose, stored in your muscles and liver as glycogen. Later, your body rebuilds its stores of glycogen by taking glucose from the blood. For up to 24 hours, your body needs the glucose you get from meals to fill up your glycogen stores. Your health care team can suggest at what times you should do extra checks to avoid low blood glucose.