Normally, insulin is released from the pancreas when the amount of sugar (glucose) in the blood increases, such as after eating. Insulin stimulates the liver and muscles to take in excess glucose. This results in a lowering of the blood sugar level.
When exercising, the body needs extra energy or fuel (in the form of glucose) for the exercising muscles. For short bursts of exercise, such as a quick sprint to catch the bus, the muscles and the liver can release stores of glucose for fuel. With continued moderate exercising, however, your muscles take up glucose at almost 20 times the normal rate. This lowers blood sugar levels.
But intense exercise can have the opposite effect and actually increase your blood glucose levels. This is especially true for many people with diabetes. The body recognizes intense exercise as a stress and releases stress hormones that tell your body to increase available blood sugar to fuel your muscles. If this happens to you, you may need a little bit of insulin after intense workouts.
For a variety of reasons, after exercise, people with diabetes may have an increase or a decrease in their blood sugar levels.