Aerobic exercise -- defined by the American College of Sports Medicine as any continuous, rhythmic activity that uses large muscle groups -- can cause adaptations that lead to increased cardiovascular health. Cycling, skating, jogging, brisk walking and swimming are all aerobic exercises. Among other effects, aerobic activity increases the cardiac output -- or blood flow -- from the heart.
Cardiovascular System Features
The main function of the cardiovascular system is to pump oxygen and blood to the tissues of your body. It is a two-way process, with the arterial system carrying blood from your heart to your organs and your venous system carrying blood back to your heart. According to website Ultimate Exercise, the process can be influenced by the fact that blood vessel capacity can change, affecting the resistance that your heart pumps against, in turn affecting the volume of blood being pushed out from your heart.
Cardiac Output
Cardiac output is the amount of blood pumped by the heart in one minute, measured in liters per minute. According to "Essentials of Strength Training and Conditioning;" by Thomas Baechle and Roger Earle, cardiac output is determined by the stroke volume -- the quantity of blood ejected with each beat -- measured in milliliters of blood per beat and multiplied by the heart rate, which is measured in beats per minute. When you go from being at rest to exercising aerobically, your cardiac output increases dramatically at first, then increases more gradually and eventually reaches a plateau. Baechle and Earle note that intense exercise can raise your cardiac output to four times its resting level, from roughly 5 liters a minute to 20 to 22 liters per minute.
Heart Rate and Stroke Volume
Raising either your heart rate, stroke volume or both increases cardiac output. Not only does your heart rate increase during exercise, but it also speeds up before you even begin, a phenomenon that Sports Fitness Advisor says is caused by the anticipatory response. The website adds that heart rate increases in proportion to your exercise intensity until your maximum heart rate -- estimated as 220 minus your age -- is reached. Following an exercise session, heart rate remains elevated, then returns to resting levels. Stroke volume increases with exercise as well, reaching up to 40 to 60 percent of maximal capacity before reaching a plateau.
Effects of Training
The demands of repeated exercise cause adaptations in the cardiovascular system. According to Sports Fitness Advisor, heart mass and volume increase; physically fit individuals also have decreased resting heart rates and greater stroke volumes. In addition, training causes increased blood supply to the skeletal muscles due to an increased number of capillaries, easier access to capillaries, increased blood volume and more efficient redistribution.
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