Physical fitness is the ability to perform vigorous physical activity. It is not measured in terms of achieving specific motor skills, but rather it is assessed in terms of muscle strength, endurance, and flexibility. The circulatory and respiratory systems are also involved because of their role in supplying muscles with blood and oxygen.

In considering muscles, strength is the maximum force that can be exerted by a muscle, and endurance is the ability to perform a muscular activity at less than maximum force, for example, in doing a series of chin-ups. Flexibility is the ability of a joint to move through a normal range of motion. The components of physical fitness (strength, endurance, flexibility, and capacity of circulatory and respiratory systems) can only be maintained through regular exercise.

Although the percentage of body fat is not a main factor in physical fitness, it must be considered...