Muscles can obtain the carbohydrate they need, not only from glycogen stores but also from sugar taken during activity, which elevates blood glucose and enhances endurance. Normally, insulin stimulates all the tissues of the body to drain glucose from the blood and store it; however, this is exactly the opposite of what is needed for performance. During physical activity, the body’s release of the hormone epinephrine keeps insulin from rising in response to glucose entering the blood. Physical activity also enhances muscle sensitivity to insulin so that the muscles become the primary recipient of blood glucose. Consuming sugar is especially useful during exhausting endurance activities lasting more than an hour. Endurance athletes often run short of glucose by the end of competitive events, and they are wise to take light carbohydrate snacks or drinks periodically during activity. During the last stages of an endurance competition, when glycogen is running low, glucose consumed during the event can make its way slowly from the digestive tract to the muscles and increase the body’s supply of glucose enough to prevent exhaustion.