Cardiorespiratory endurance is the ability of the heart and lungs to absorb, transport, and utilize oxygen over an extended period of physical exertion. As one of the four primary components of physical fitness, it is an important measure of the overall health and fitness. Age, genetics, and physical conditioning all play a role in an individual's cardiorespiratory endurance.
A number of biophysical tests, including maximum volume of oxygen consumption (VO2Max,) heart rate monitoring, and shuttle run tests are used to measure cardiorespiratory endurance. A very fit individual will be able to perform exercise at a greater intensity, over a longer duration, while consuming a smaller volume of oxygen than a less fit person. Regular participation in aerobic activities will usually improve performance on physical tests.
Cardiorespiratory endurance is a function of both genetic potential and physical adaptation. Enacting an aerobic training program can increase endurance by strengthening the heart muscle and increasing lung volume. With an enhanced ability to take in oxygen and deliver it to working muscles, the muscles are able to continue activity longer without fatigue.
Physical conditioning creates cardiorespiratory adaptations on a microscopic level as well. The lungs themselves and the muscles they service are equipped with a dense network of capillaries for gas exchange. Regular aerobic exercise will increase the density of this network, increasing oxygen availability.
Additionally, aerobic training will increase the size and number of mitochondria in each muscle cell. The mitochondria utilize oxygen to liberate energy from food nutrients. An increase in the number of these cellular energy factories means that the cells are better able to efficiently utilize the delivered oxygen to power muscular activity.
Cardiorespiratory training is usually focused on achieving and maintaining a predetermined percentage of maximal heart rate. Maximal heart rate is calculated by subtracting age from 220. Training programs usually involve 15 to 60 minutes of continuous activity at 40 to 85% of maximal heart rate, with less fit individuals working at the lower end of each range, and increasing time and intensity with improved fitness.
Novice activities for cardiovascular conditioning include walking, stationary cycling, swimming, and water aerobics. As fitness increases, cardiorespiratory endurance can be improved through light jogging and group fitness classes. Once a high level of conditioning is attained, advanced athletes can work to increase VO2Max, and prepare for competitive sports by using complex movements, interval training, and cross-training programs working near the anaerobic threshold.