What is Cardiorespiratory Fitness?

culled from:www.articleworld.com

Cardiorespiratory fitness is a measure of how well your body is able to transport oxygen to your muscles during prolonged exercise, and also of how well your muscles are able to absorb and use the oxygen, once it has been delivered, to generate adenosine triphosphate (ATP) energy via cellular respiration (cellular respiration is a chemical process in your body's cells that converts the energy stored in the food you eat into the ATP form of energy that is recruited for use by your muscles). Essentially, your cardiorespiratory fitness level is a measure of the strength of your aerobic energy system. If you haven't already read the Exercise Energy Systems article you can do so to get a better understanding of what ATP is, what cellular respiration is, and what the aerobic energy system is (in addition to your body's other two energy systems).
The Basic Physiology of Cardiorespiratory Fitness
According to the definition of cardiorespiratory fitness provided above, it can be broken down into two components. The first component of cardiorespiratory fitness is the ability of your body to transport oxygen to your muscles during prolonged exercise. The second component of cardiorespiratory fitness is the ability of your muscles to absorb and use oxygen while you are exercising. We'll examine each component in more detail.
Let's discuss the first component of cardiorespiratory fitness. Your body's ability to transport oxygen to your muscles is dependent on the coordinated activities of your heart, arteries, veins, and lungs. The process works like this:
1.    You breathe air into your lungs. The oxygen in the air you breathe is absorbed into the blood in the capillaries that surround your lungs and then transported via the pulmonary vein into the left side of your heart.
2.    The oxygenated blood is pumped out of the left side of your heart and into the arteries that deliver it throughout your body to your muscles.
3.    When the oxygenated blood reaches your muscles the oxygen is absorbed into your muscle cells from the blood capillaries that surround them. At the same time that your blood is providing oxygen to your muscles, it is also removing carbon dioxide, a waste product from muscle cellular respiration, from them. The now de-oxygenated and carbon dioxide rich blood is returned to the right side of your heart via your veins.
4.    The de-oxygenated and carbon dioxide rich blood is pumped out of the right side of your heart to your lungs via your pulmonary artery. Once in the lungs, your blood rele