These components are: cardiorespiratory endurance; muscular strength; muscular endurance; body composition; and flexibility. In order for a person to improve his or her overall level of physical fitness, he or she must work on improving all five of these components.
Regarding the first of these components, cardiorespiratory endurance can be defined as the ability of the body's circulatory and respiratory systems to supply fuel during sustained physical activity (Eijnde & associates, 2003). This component of physical fitness can be improved by activities that maintain an elevated heart rate at a safe level for a sustained period of time. Exercise techniques and methods for improving cardiorespiratory endurance include activities such as walking, swimming or bicycling (Petrie, Matthews & Howard, 1996).
However, it is important to recognize that whatever exercises are chosen to improve cardiorespiratory endurance, they need not be strenuous. As noted by Nielens and Plaghki (2001), even patients who are in a good deal of pain, which makes activities associated with cardiorespiratory endurance difficult, can make good progress if they start out slow and work up to a more intense pace. There are, however, indications that there may be some differences in men and women in this regard.