Physical activity can significantly reduce the risk of coronary artery disease. This may be related to the fact that exercise often helps in maintaining a healthy weight, as well as safe blood pressure and cholesterol levels. Physiologically speaking, there are two kinds of exercise: anaerobic and aerobic. Anaerobic activities include physical work of short duration that does not force the body's metabolism to mobilize fat reserves, increase oxygen uptake, or increase heart output. Instead, the body provides energy for the activity out of readily available carbohydrates. Low-intensity weight lifting is an anaerobic exercise, as are the first few minutes of aerobic exercise sessions prior to the metabolism conversion. However, if the same work is performed continuously, especially at a steady level of intensity, the metabolism converts to an aerobic exercise mode. Aerobic exercise includes activities that use the body's large muscle groups continuously to force an increase in the heart's blood output and the lung's oxygen intake, using oxidized (OX-ih-die-zd) carbohydrates and stored fats as the energy source. In order to functionally benefit the heart and lungs, this period of time usually equals a 30 to 60 minute session of continuous activity, three or more days per week. Running, jogging, swimming, bicycling, brisk walking, and cross-country skiing are all examples of such training. In general, habitual aerobic exercise can benefit the cardiovascular (kar-dee-oh-VASK-you-lar) system in numerous ways. It helps train the heart muscle to pump more blood per minute, while also putting out more blood with each beat. Further, it can enable the blood to carry more oxygen, while also increasing overall blood volume. Exercise may enlarge the lung's capacity for oxygen consumption, and thus better the body's heart and lung teamwork or cardiovascular-cardiorespiratory (kar-dee-oh-VASK-you-lar kar-dee-oh-RES-preh-tore-ee) function. Over time, adequate aerobic exercise can also improve the ability of the body's muscles to extract oxygen from the blood and use it for performing their work. This exercise training includes the heart muscle or myocardium (my-o-KAR-dee-um). In other words, the heart may begin to work more efficiently, demanding less oxygen than previously for the same amount of work. This improvement may even positively affect coronary artery disease, because the heart performs at a higher rate for a longer time, without causing myocardial ischemia (my-oh-KAR-dee-uh iss-KEEM-ee-uh), or insufficient oxygen supply. If you're interested in beginning an exercise program, or have questions about aerobic and anaerobic exercise, contact a healthcare provider.