What Is Cardiorespiratory Fitness?

Cardiorespiratory (cardio meaning heart and respiratory meaning lungs) fitness is the ability to utilize large muscle groups for physical activity at a moderate or high intensity or prolonged periods of time. Some may refer to this as cardiovascular (meaning the heart and blood vessels) fitness as well. These terms are often used interchangeably.

The cardiorespiratory system, which includes the heart, the lungs, blood vessels, circulatory system, and the blood, is extremely important. This system must reach every cell in the body. It has to constantly respond to any changes within the body in order to keep all the organs and systems functioning properly. Whether exercising or at rest, this system constantly works to meet the demands of your bodily tissues.

The Basics of Cardio

Activities such as brisk walking, running, cycling, swimming, and cross-country skiing are all associated with cardiorespiratory fitness. Consider for a moment what would happen if you were to go outside and simply begin to run. Consider what the affects of such activity would be on your body.

As you run, your heart rate would begin to speed up; you would realize that your breathing is faster. As you continue to run, your heart beats not just faster but harder, and you may find it harder to breathe. These are normal physiological responses to running. Why does your heart rate increase? Why does your breathing become labored?

Oxygen and Your Body

Whenever you go for a run, your muscles have to contract with more force and at a faster rate than when at rest. The only way your muscles can contract is if they've been provided the necessary oxygen by your blood. No oxygen, no work — it's pretty simple. So where does the oxygen come from?

Not to state the obvious — but this is what your lungs are for. Your heart pumps blood to your lungs, where it picks up oxygen molecules. The heart then pumps that oxygenated blood back out to the rest of your body where it travels through the blood vessels to your working muscle cells. Oxygen is released to those cells, which allows them to continue to contract. The deoxygenated blood is then pumped back to your heart, and the cycle repeats (in fact, this cycle never stops for as long as your heart is still beating). With regular cardiorespiratory (CR) training, the oxygenation process becomes more efficient. As you train, the nine-minute mile you may have run this week will start to feel less difficult three weeks from now.

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