The cardiovascular system includes your heart, lungs and blood vessels.
During exercise, the job of the cardiovascular system is to deliver blood and oxygen from the heart and lungs to your working muscles. Oxygen is needed for many types of exercise. Your blood carries nutrients to your muscle cells to create energy that your muscles need to contract. Aerobic exercise is defined as physical activity that is rhythmic, involves large muscle groups and is sub-maximal in intensity. During a single bout of aerobic exercise, your cardiovascular system responds to meet the increased oxygen need of your muscles.
The cardiovascular system increases your heart rate and shunts more blood to your muscles during exercise.
Create a Deficit
When you start aerobic exercise, your body immediately senses a need for increased oxygen and starts taking steps to get more oxygen into your body and then delivered to your muscles. However, these physiological responses can take up to four minutes to rev up your metabolism in order to meet the new oxygen demands. During this time, your body is using your anaerobic systems to create energy. These systems can only produce energy for a short period of time. At sub-maximal intensities, aerobic metabolism takes over to produce energy in the presence of oxygen. During the first few minutes of exercise, as your body tries to meet your new oxygen needs, you are in a state of oxygen deficit. Therefore, you may feel winded for the first few minutes of exercise until your body adjusts.
Meet the Need
In order to meet oxygen and energy needs during aerobic exercise, and overcome your oxygen deficit, the cardiovascular system goes through some changes from your normal resting state. Your cardiac output is influenced by your heart rate and stroke volume. Stroke volume is the amount of blood that is pumped out of your heart with each beat. Both your heart rate and stroke volume increase during exercise which increases your cardiac output. Your respiration, or breathing rate, is also increased to bring more oxygen to your lungs.
Redistribute the Blood
During exercise, your systolic blood pressure also increases and plays an important role in your blood distribution. Some of your blood vessels can contract or relax. The vessels that deliver blood to active tissues during exercise, such as your muscles, will actually dilate. This allows more blood to flow to your muscles. During exercise, less blood is needed in organs such as your stomach and intestines, and therefore, some of those blood vessels will constrict.
The After Effect
When you stop exercising, although your oxygen requirement goes back to your resting level, your cardiovascular system takes some time to get back to normal. While your respiration, blood pressure and cardiac output will slowly decrease, they all remain above resting levels during a recovery period in order to remove exercise byproducts such as lactic acid from your blood and restore your normal conditions. This elevated state of metabolism is referred to as excess post-exercise oxygen consumption. The higher the intensity of your exercise, the greater the after effect your body will have. This means you will burn additional energy, or calories, during your recovery period.