What is physical fitness?
The simplest, most practical definition of physical fitness is the ability to respond to routine physical demands with enough reserve energy to cope with a sudden challenge. You can consider yourself fit if you meet your daily energy needs, can handle unexpected extra demands, have a realistic but positive self-image, and are protecting yourself against health problems, such as heart disease.
Fitness consists of three basic components: flexibility, cardiovascular or aerobic fitness, and muscular strength and endurance. Other factors, such as body composition and agility, also may be considered in assessing overall fitness. However, if you focus on the three basic components of physical fitness, your body will operate at maximum capacity for as many years as you live.
Flexibility is the range of motion around specific joints—for example, the stretching you do to touch your toes or twist your torso. Flexibility depends on many factors: your age, gender, and posture; bone spurs; and how fat or muscular you are. As children develop, their flexibility increases until adolescence. Then a gradual loss of joints mobility begins and continues throughout adult life. Both muscles and connective tissues, such as tendons and ligaments, shorten and become tighter if not used at all or not used through their full range of motion.
Cardiovascular fitness refers to the ability of the heart to pump blood through the body efficiency. It is achieved through aerobic exercise—any activity, such as brisk walking or swimming, in which the amount of oxygen taken into the body is slightly more than, or equal to, the amount of oxygen used by the body. In other words, aerobic exercise involves working out strenuously without pushing to the point of breathlessness. Anaerobic exercise is any activity in which the amount of oxygen taken in by the body cannot meet the demands of the activity; there is thus an oxygen deficit that must be made up later. An example of an anaerobic exercise is sprinting the quarter-mile, which leaves even the best-trained athletes gasping for air.
Strength—the absolute maximum weight that we can lift, push, or press in one effort—is what most of us equate with muscular fitness. However endurance—the ability to keep lifting, pushing and pressing—is just as important. It’s not enough to be able to hoist a shovelful of snow; you've got to be able to keep shoveling until the entire driveway is clear.