Physical Fitness Definition

Our physical fitness definition is very much oriented towards functional ability. We see it as the ability to meet physical challenges, whether related to work, sport, recreation, combat, or other life activities. A man’s physical fitness must be seen in the context of the specific physical challenges he is likely to face. Thus the criteria for a physically fit firefighter, policeman, or combat soldier are by necessity much more stringent than those for an elderly, frail man who is challenged by daily activities such as climbing stairs, taking out the trash or even getting up out of a chair.

There are several components of physical fitness including some that are not readily improved by training, such as coordination, reaction time, peripheral vision, and height. Since little or nothing can be done to improve these, our physical fitness definition below includes only physical capabilities that are amenable to training. These are strength, muscular endurance, aerobic endurance, speed, agility/quickness, flexibility, and balance:

  • Strength
    Strength is an important aspect of our physical fitness definition, and is the ability to exert force. The strength required of a sport or other physical activity is specific to the movements involved and the speed at which force must be exerted. For example, a tennis player exerts force at high speeds against the relatively low inertial resistances of his body, the racket and the ball, while a football lineman must exert high force against an opposing player at movement speeds restricted by the other players resistance. That is why these athletes have very different kinds of bodies and must train differently to produce optimal performance.

  • Muscular Endurance
    Muscular endurance is the ability of muscles to repeatedly exert a specified amount of force that is less than maximum. Generally, men who can exert higher maximal force can also do more repetitive movements at a given resistance. For example, a man who can lift a maximum of 100 lbs can generally do more repeated lifts with 50 lbs than a man who can lift a maximum of 80 lbs. However, athletes trained and suited for endurance sports can usually do more repetitions with a given percentage of their maximum lifting capability than those athletes trained and suited for sports requiring high strength. From another point of view, strength athletes have a higher maximum lift than would be predicted by the number of repetitions they can do with a lighter weight while endurance athletes have a lower maximum lift than would be predicted.

  • Aerobic Endurance
    Aerobic endurance must be included in any physical fitness definition. It is the ability to sustain large-muscle physical activity over time periods ranging from several minutes to several hours. Such activity is largely fueled by the aerobic (oxygen-utilizing) metabolism of carbohydrates and fats. Thus, the rate (e.g. running speed) at which such activity can be sustained largely depends on the rate at which oxygen can be delivered to the muscle cells and processed to produce energy. This in turn is dependent on the rate at which the heart can pump blood (heart rate times volume pumped per beat), the hemoglobin (oxygen-carrier) content of the blood, and the rate at which the mitochondria, the muscles' energy factories, can break down carbohydrate and fat to produce energy, carbon dioxide and water.

  • Speed
    Speed is a key component of a physical fitness definition because of its wide application to many human activities. It is the maximal velocity that can be reached by part or all of the body. The speed of a sprinter is greater than that of a distance runner, although the distance runner can sustain his speed much longer. In some sports, the body as a whole does not move fast, but a part of the body does. In baseball pitching, for example, the hand and ball accelerate to great speed while the body as a whole barely changes its location.

  • Agility/Quickness
    Another component in our physical fitness definition is agility. It is the ability to rapidly change the body’s momentum from one direction to another. This requires either acceleration in any direction from dead stop or deceleration in the direction one is traveling and acceleration in a new direction. Based on Isaac Newton’s second law, acceleration/deceleration is proportional to the ratio of force to mass. Thus, if two men can exert equal force on the ground, the one with a lower body mass will show greater acceleration. From another point of view, if two individuals have the same body mass, the one who can exert more force on the ground will show greater acceleration. In addition to the ability to accelerate, agility requires a certain degree of flexibility, which aids in going over, under, and around obstacles.

    "Quickness" is a colloquial term referring to the ability to accelerate. It differs from “agility” in that “quickness” sometimes refers to the ability to accelerate in one direction only, while agility always implies the ability accelerate in multiple directions. A sprinter who gets off the starting blocks first is referred to as “quick.” However, he may be caught over the race distance by an opponent who is not as “quick” but who reaches a greater top speed. For example, Usain Bolt, the current top sprinter in the world, doesn’t get out of the blocks as fast as some of his opponents but he reaches a higher top speed and usually runs them down.

  • Flexibility
    Flexibility refers to the range of motion through which a body joint can be flexed or extended and the ease with which this is accomplished. Some activities like ballet, gymnastics, and Olympic weightlifting require excellent flexibility, while most daily life activities and many sports such as football and boxing do not require great flexibility. More flexibility is not always better. People who are extremely flexible may be susceptible to joint injuries, while those who are less flexible risk muscle injury.

  • Balance
    Balance is the ability to maintain desired body posture and position while standing or moving on a stable or unstable surface. As beings who stand and move on two legs we have complex mechanisms to keep our balance. Yet balance varies among individuals and tends to decline with age.

NOTE: Some sources include body composition and power in their physical fitness definition. We do not include these for the following reasons:

  • We consider body composition more related to health than to physical fitness. Some men with excess body fat can nevertheless perform at elite athletic levels. High body weight may even aid some athletes to perform (e.g. Sumo wrestlers, football lineman). Yet despite being physically fit for the challenges they face, such athletes may be at increased risk for disease.

  • We do not differentiate power from strength. "Power" is often used to mean the ability to accelerate the body or a sports implement. However, acceleration requires force, and strength is the ability to exert force. Thus, instead of placing power in its own physical fitness category, we refer to speed-strength, which is the ability to increase force quickly and continue exerting force as the body or implement reaches high speeds.

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