Exercise and physical fitness provide numerous benefits for your mind and body. Though it may sound like a paradox, being active can actually give you more energy. That's because it increases muscle endurance and lung capacity, and helps your heart work more efficiently. In turn, your body does a better job of circulating blood and oxygen. Exercise is also noted for its ability to combat stress. Doctors believe that vigorous activity can cause the release of certain feel-good chemicals. One such substance is beta-endorphin (BAY-tuh in-DOOR-fin), a natural mood-enhancer, which may appear in the blood after as little as twelve minutes of exercise. Other researchers speculate that being active increases your level of serotonin (sair-uh-TOE-nin), another naturally-occurring substance that produces a feeling of well-being. Over the long term, physical fitness may even extend your life, as compared to those who lead a sedentary lifestyle. The biggest gains occur when you work out strenuously, meaning at least two hours of aerobic activity a week. However, even moderate exercise can lower your chance of heart disease and other problems. To find out more about the advantages of being fit, speak to a health care professional.