The term components of fitness refers to the several key components required to facilitate quality overall fitness. In most traditional circles, there are considered to be five general components of fitness: strength, endurance, flexibility, power, speed, 22.214.171.124 11:38, July 4, 2011 (UTC), coordination, accuracy, Reaction time and agility. however, some also contend that it is a type of speed, i.e. "reaction speed". Improvements in endurance, stamina, strength, and flexibility come about through conditioning/training. Training refers to activity that improves performance through a measurable organic change in the body. Concurrently, improvements in coordination, agility, balance, and accuracy are developed through practice. Practice refers to activity that improves performance through changes in the nervous system.Edit
The components of fitness each work together to contribute to the ability of the body to handle physical demands. The more efficient the body functions, the higher the level of fitness. Optimal fitness is a combination of lifestyle, nutrition, habits, but it cannot be reached without an appropriate level of physical activity. Optimum physical performance is a combination of all the components of fitness; depending on the specific demands of the sport or activity, some components will require more attention than others, but each should be present as a part of an integrated training program.
A more comprehensive and holistic view of fitness expands this to 21 Components of Fitness
General Components of FitnessEdit
Endurance is, simply put, the ability to endure, or an object or person's lasting quality. Thus, the longer a thing lasts, the greater the endurance. Endurance may refer to short-term--high intensity, anaerobic exercise such as sprinting--or long term, which may last hours or even days in duration, as in the case of marathons, triathlons, and ultramarathons.
In terms of fitness, endurance may be broken down into several types: aerobic endurance (cardiorespiratory endurance), anaerobic endurance, speed-endurance and strength-endurance. It is most commonly broken up into cardiorespiratory endurance and muscular endurance.
Well-trained endurance athletes are able to generate blood lactate levels that are 20-30% higher than those of untrained individuals under similar conditions. This produces significantly enhanced endurance as their muscles are better equipped to utilize it to fuel further muscular energy.
Cardiorespiratory endurance refers to the efficiency with which the body delivers oxygen and nutrients needed for muscular activity and transports waste products from the cells. It is also sometimes referred to as aerobic endurance or aerobic fitness. Improving aerobic endurance enables the heart, lungs, and muscles to do work over a longer period of time. Cardiorespiratory conditioning can decrease risk factors associated with heart disease, increase vitality, increase maximum oxygen uptake, and can aid weight loss or maintenance.
In addition to this, training cardiorespiratory endurance improves aerobic capacity caused by fibre adaptation, more specifically an increase in the size of mitochondria, which enhances the ability of the fibres to generate aerobic energy. It also facilitates an increase in capillary density, which enhances the fibres’ capacity to transport oxygen, and thus to create energy. Finally, endurance training increases the number of enzymes relevant to the Krebs cycle, a chemical process within muscles that allows the regeneration of ATP under aerobic conditions. The enzymes involved in this process may actually increase by a factor of two to three after a sustained period of endurance training.
Muscular endurance, or stamina, is ability of body systems to process, deliver, store, and utilize energy.
Flexibility refers to the movement in a joint or group of joints, during a passive movement (passive meaning no active muscle involvement is required to hold the stretch; instead gravity or a partner provides the force for the stretch). Flexibility is a general component of physical fitness. Additionally, good range of motion will allow the body to assume more natural positions to help maintain good posture. This component becomes more important as people age and their joints stiffen up, preventing them from doing everyday tasks. Stretching is therefore an important habit to start and continue as one ages. Flexibility of a joint depends on many factors, particularly the length and looseness of the muscles and ligaments due to normal human variation, and the shape of the bones and cartilage that make up the joint. The primary reasons for increasing flexibility are enhanced performance and reduced risk of injury. The rationale for this is that a limb can move further before an injury occurs.
Strength is recognized as the ability to exert force, typically measured in the amount of weight a person can lift or manipulate. There are five broad categories of strength, each with its own special training requirements: absolute, limit, speed, anaerobic, and aerobic.  There are many factors that influence strength.
- Structural/Anatomical - muscle fiber arrangement, musculoskeletal leverage, ratio of fast vs. slow-twitch fibers, tissue leverage, scar tissue and adhesions (motion-limiting factors), elasticity, intramuscular/intermuscular friction, etc.
- Physiological/Biochemical - stretch reflex, Golgi tendon organ sensitivity, hormonal function, energy transfer systems efficiency, extent of hyperplasia, myofibrillar development, motor unit recruitment, cardiovascular and cardiorespiratory factors, etc.
- Psychoneural/Learned Responses - arousal level, pain tolerance, level of concentration, social learning, skill level, spiritual factors, etc.
- External/Environmental - equipment, weather, altitude, gravity, opposing/assisting forces, etc. 
Muscular strength is a general component of fitness. Strength level should only be to a point where the increased strength will not interfere with technique execution. When excessive amounts of strength are developed, range of motion, and speed of execution is decreased and coordination usually deteriorates. Thus, it becomes increasingly important to keep all of these factors well balanced.
Components of Motor FitnessEdit
Accuracy is the ability to control movement in a given direction or at a given intensity.
Agility is the ability to apply explosive movements to rapidly change directions.
Balance is the ability to exercise precise control over the body's position and movement.
Motor coordination (sometimes called hand-eye coordination) is the coordinated functioning of muscles or groups of muscles in the execution of a complex task. Coordination itself, however, is a global system made up of several synergistic elements and not necessarily a singularly defined ability. Coordination is, in essence, the ability to integrate all the components of fitness so that effective movements are achieved. Rhythm, spatial orientation and the ability to react to both auditory and visual stimulus have also been identified as elements of coordination.
Motor coordination can be broken into two components: gross motor coordination and fine motor coordination. Gross motor coordination refers to gross motor skills, such as walking, running, climbing, jumping, etc. Fine motor coordination refers to fine motor skills, such as drawing, writing, typing, etc..
In reference to athletic performance, gross motor coordination may entail more complex movements than simply walking, jumping, or running. Athletic coordination is the ability to combine several distinct movement patterns into a singular distinct movement.
Power, in physics, is the "rate at which work is performed," i.e. work is the "product of force and distance" (Work = Force x Distance).  What this usually translates to is the ability to exert maximum muscular contraction instantly in an explosive burst of movement, ie. the ability of a muscular unit, or combination of muscular units, to apply maximum force in minimum time. The two components of power are strength and speed, as with power exercises. (e.g. jumping or a sprint start, snatch, clean and jerk, etc.)  Power is a vital component of motor fitness, and is applicable especially to a myriad of athletic activities, and therefore it should not be neglected. Despite the importance of power for athletics and function, the ability to produce powerful muscle contractions decreases with age, more so than other components, such as cardiorespiratory endurance. This decline also appears despite persistent training and otherwise good health.
Speed is the rate of motion, or equivalently the rate of change in position, often expressed as distance traveled per unit of time. A subcategory of speed is quickness, which is the ability of the central nervous system to contract, relax or control muscle function without involvement of any preliminary stretch.
Reaction time is the interval time between the presentation of a stimulus and the initiation of the muscular response to that stimulus. A primary factor affecting a response is the number of possible stimuli, each requiring their own response, that are presented.  Examples include how fast a sprinter can get off the blocks and react to a gun, how quickly a boxer can react to an opponent's punch, or how quickly a batter can recognize and respond to a pitch.
A subcategory of speed is quickness, which is the ability of the central nervous system to contract, relax or control muscle function without involvement of any preliminary stretch. Quickness is measured as the time interval or reaction time between voluntary stimulation and the initiation of movement. This time should be distinguished from absolute movement speed, which is the interval from the beginning to the end of movement.
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