Cardiorespiratory fitness refers to how well the body can move oxygen from blood to muscles during prolonged physical exercise. Absorption of oxygen and generation of adenosine triphosphate (ATP) by muscles is also referred to as cardiorespiratory fitness. ATP is used for cellular activity in the body when cellular energy levels are low. In a fitness setting, cardiorespiratory fitness is often broken down into transportation of oxygen and absorption and use of oxygen.
Transportation of oxygen starts during inhalation. Oxygen is taken into the lungs and absorbed by capillaries. Once oxygen passes through the heart, it is pushed out to various muscles and organs, where oxygen is absorbed before the blood returns to heart and eventually back to lungs for more oxygen. The first stage of cardiorespiratory fitness measures how effective this process is in the body.
When oxygen reaches muscles, the second stage of cardiorespiratory fitness begins. Muscles must work to absorb oxygen and generate ATP. More muscles in a given area typically mean more capillaries. Additional capillaries can improve this type of fitness. Once absorbed, mitochondria transform that oxygen to ATP. Mitochondria are small organelles responsible for various aspects of cell health and energy production.
Building cardiorespiratory fitness involves building more muscle tissue and increasing lung capacity through aerobic and anaerobic activity. Aerobic activity refers to exercise requiring frequent oxygen exchange, such as running, jogging, or swimming. Anaerobic activity does not require high levels of oxygen. These exercises can include weight training and stretching.
Aerobic and anaerobic activity work together to increase cardiorespiratory fitness. Aerobic activity may help to increase lung capacity and transportation of oxygen from lungs to blood. Anaerobic activity works to increase muscle mass for additional oxygen absorbing capillaries, and better effectiveness of oxygen absorption.
There are three common forms of cardiorespiratory exercise — simple, moderate, and uncontrolled. Simple exercises include walking, jogging, and elliptical training. Moderate exercises include swimming, in-line skating, and jumping rope. Uncontrollable exercises may be more fun, but heart rate and intensity is often dependent on individual situation and skill level. These exercises can include basketball, baseball, and volleyball.
Cardiorespiratory fitness typically responds to working out 20 to 60 minutes per session. It is important to maintain energy levels and attention to exercise during activity, to increase fitness levels and decrease chance of injury. Some beginners find it easier to break up exercise into two to three smaller sessions per day. For instance, working out three times a day for 10 minutes is the same as 30 minutes of exercise.