Your cardiorespiratory system oxygenates the blood, then delivers this blood to the cells of your body that need it most. Oxygen is necessary for energy production within the cell so this cycle is important. In addition, carbon dioxide, a byproduct of cellular energy production, is removed and excreted. First, your lungs take in oxygenated air and release carbon dioxide. Next, your heart pumps blood out to the body via the blood vessels around your periphery. Exercise challenges this system, causing it to adapt in a healthy way.
Heart
When you exercise for fitness, your heart must work harder. It needs to give your body more blood than at rest. It does this by increasing its heart rate and stroke volume. Your heart rate can increase from 60 to 100 bpm at rest up to or exceeding 200 bpm with maximal exercise. The amount it increases varies upon your age and fitness level. Your heart also increases the amount of blood it ejects per beat, also called stroke volume. With regular exercise, your heart becomes a more efficient machine. Changes including the size of your ventricles and a reduction in resting heart rate indicate an increase in cardiorespiratory fitness that allows your heart to provide your body the blood it needs. This reduces your resting heart rate and allows you to work at even higher intensities.
Lungs
Your lungs are never really the limiter when it comes to exercise. They have a phenomenal capacity for meeting your body's oxygen demands during exercise. One adaptation that makes it easier for your lungs to function during exercise is the musculature surrounding your lungs. The diaphragm, abs, intercostals, traps, scalenes and sternocleidomastoid aid in inspiration and exhalation during exercise. With regular training the structure and function of these muscles improve, allowing your lungs to take more air in and out with each breath.
Blood and Vessels
Your bloodstream is a part of your cardiorespiratory system. It's flow and volume changes with your level of fitness as well. With regular exercise, your body increases its capillarization. This means your body lays new capillaries around the working muscles, allowing for a larger area of access for blood to flow. Your body also becomes better able to use the oxygen inside your bloodstream. Cardiorespiratory fitness means your arteriovenous oxygen difference increases, marking more oxygen used by your muscles. Finally, your blood volume increases. A larger volume means more blood is available to more parts of your body making exercise easier and marking an increase in cardiorespiratory fitness.
Recommendations
Cardiorespiratory fitness gains can come without weight loss and it may be easier than you think. In 2007 the American College of Sports Medicine and the American Heart Association released exercise guidelines for improving cardiovascular fitness and health in the journal "Circulation." According to these institutions, to improve your health, you must work at a moderate intensity for 30 minutes at least five days per week. More gains will be seen with more exercise and a higher intensity.
References
- Sporting Performance; The Cardiorespiratory System; 2005
- "Exercise Physiology: Human Bioenergetics and Its Applications"; George A. Brooks, et al.; 2005
- SportsFitnessAdvisor.com; The Cardiovascular System and Exercise; Phil Davies, CSCS
- Lewis Clark State College: Cardiovascular and Respiratory Adaptations to Training
- "Circulation"; Physical Activity and Public Health: Updated Recommenations For Adults From The American College of Sports Medicine and the American Heart Association; William L. Haskell, PhD, et al.; 2007
