The cardiovascular system serves several important functions in the body.
For example, it delivers oxygen and nutrients to and removes carbon dioxide and metabolic waste products from every cell in the body. Your body's cardiovascular system has three components:
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The heart (cardiac muscle)
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The blood vessels
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The blood
The heart is the pump that moves blood from the lungs (where the blood picks up oxygen) to the muscles (which burn the oxygen as fuel) and back to the lungs again. The harder you are training, the more fuel your muscles need and the harder your heart has to work to pump oxygen-rich blood to the muscles.
As you get more fit, your heart is able to pump more blood with every beat. As a result, your heart doesn't have to beat as often to get the needed oxygen to your muscles - so both your resting heart rate and your exercise heart rate (at any given exertion level) decrease.
Heart rate is one of the simplest and most informative of the cardiovascular parameters. When you start training, your heart rate increases rapidly in proportion to the intensity of the training. In Polar Heart Rate Monitors the transmitter in the belt detects the electrocardiogram (ECG), the electric signal originating from your heart. The transmitter then sends an electromagnetic signal to the Polar wrist receiver, which shows you information about your heart rate.