Glucose is the fuel that muscles use to keep you going. You know that the glucose form the food you eat makes its way into the blood. This is what you measure when you do a blood glucose test. But glucose can also be found in your muscles. Your muscles keep plenty of glucose, stored as glycogen, ready to use for energy.
When you first start exercising, your body uses the glucose stored in your muscles and liver as glycogen for fuel. When these stores of glucose run low, your muscles recruit the glucose from your blood. So, during exercise, your blood glucose levels can fall. After your stop exercising, your body replenishes the stores of glucose in the liver and muscle cells. This can further lower blood glucose levels even hours after you have stopped exercising. Because of this, if you exercise in the evenings, you leave yourself vulnerable to hypoglycemia while you sleep. Even though regular exercise can be a good tool for lowering blood glucose levels, it also puts you at risk for hypoglycemia. This is why monitoring blood glucose levels before and after exercise works to keep you in the game. Exercise-induced hypoglycemia is a concern for people who take insulin or a sulfonylurea. Whether taking metformin puts you at risk for exercise-induced hypoglycemia is questionable.
Besides directly affecting blood glucose levels, exercise can also affect the action of insulin. It’s a fact that the body absorbs insulin differently from one day of the next. Similarly, exercise can affect insulin absorption. By increasing the flow of blood throughout the body, exercise speeds up how fast the insulin you inject gets to work. Injecting into an arm or leg that’s then involved in exercise can speed up insulin absorption. So, a given amount of insulin can have different effects from one day to the next, especially if there are differences in your physical activity routine. T
his makes it doubly important to check your blood glucose levels when you exercise. For people with type 2 diabetes, especially those who are controlling blood glucose levels through diet and exercise alone, big swings in blood glucose levels do not usually occur during exercise. However, if you have type 2 diabetes and are taking insulin or a sulfonylurea, your blood glucose levels may drop too low during or after exercise. Like people with type 1 diabetes, you will want to be careful to avoid hypoglycemia.