Heart and blood vessels: Your cardiovascular system transports oxygen to cells and removes carbon dioxide, carries away metabolic waste products, and shuttles hormones to the intended organs. In addition, it helps maintain body temperature and preserve your body’s acid balance. Most people can engage in light activity, about the equivalent of walking 2 mph, without placing excess demand on their circulatory and respiratory systems. When you exercise more intensely, however, your muscles’ need for oxygen increases. Your heart must pump harder and faster. The amount of blood your heart pumps and the oxygen your body consumes rise in direct proportion to the amount of work your muscles are performing. And once again, your level of physical conditioning dictates how well this system works.
Your Blood Pressure to Rise
Arteries in your working muscles dilate to accommodate their increased need for blood. At the same time, the heart’s increased output causes your blood pressure to rise. Arterioles (tiny arteries) in your skin expand, allowing for more blood flow there. As you continue to exercise, especially in hot, humid weather, more blood is diverted to your skin to maintain a safe body temperature.
While your arteries dilate, veins serving distant parts of your body contract. When you are resting, the venous system stores roughly 65% of the body’s blood supply. But when veins contract, they make more blood available to your heart and exercising muscles. Your body further optimizes the distribution of blood by limiting the amount sent to the kidneys, liver, digestive system, and other organs not immediately involved in the exercise process.
Boosting Your Cardiorespiratory Endurance
When you exercise regularly, your circulatory system adapts by boosting your cardiorespiratory endurance. Your body creates more plasma, the saltwater fluid that carries glucose and other nutrients to cells and ferries away waste. Because plasma is a component of blood (along with blood cells), a greater volume of blood is available to pump. That blood is slightly thinner than usual, which lowers the resistance it encounters while circulating. The main pumping chambers of your heart, called the ventricles, stretch to hold more blood and contract with greater force. Over the long term, the heart muscle increases in size, which strengthens the heart.
Feed The Muscles More Oxygen-Rich Blood
Likewise, the capillaries that serve the working muscles — including the heart — increase in number. These additional blood vessels serve two valuable functions. First, they feed the muscles more oxygen-rich blood. Second, the presence of more vessels means that the heart’s powerful pumping chamber, the left ventricle, has a more plentiful energy supply and is able to pump the blood with greater ease. The more efficient pumping action allows you to do more work with less effort.
The Coronary Arteries Feeding
The greater need for oxygen-rich blood that occurs during aerobic exercise can also lead to an increase in the size and number of branches of the coronary arteries feeding the heart. This provides other channels for oxygenated blood to reach heart muscle. So if an artery serving the heart becomes blocked, heart muscle damage is less likely because alternative channels keep the blood supply flowing. The boost in oxygen and other benefits of exercise offer some protection against dangerous heart rhythm disturbances as well.
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