Many people aspire to this state of physical capability, but only a small number actually achieve it. Those people who live well or comfortably are particularly prone to failure in this regard, due to contentment and subsequent inactivity, and those who live in straitened circumstances are more prone to disease, stress and poverty, all of which can work to actively prevent the achievement of physical fitness.
Physical fitness is usually defined by those humans who seek it in a fairly pragmatic way: for example "I want to be fit enough to run to catch a bus and not expire of a heart attack after doing so" is a fairly common sort of stated criterion for "fitness". Those who specialise in becoming physically fit1 for different purposes have more precise definitions, but the pragmatic effect of each definition is essentially the same: the person pursuing physical fitness defines their level of fitness by how well they are able to avoid certain, otherwise inevitable consequences of vigorous physical activity. It comes as no real surprise to learn that all definitions of fitness are relative, in this context, but definitions which are not relative are very difficult to formulate, particularly without resorting to terms of general, all-body well-being which are usually so vague as to make the defintion inapplicable to almost everyone individually. For this reason, most definitions concentrate more on what fitness enables you to do in strictly operational terms2 rather than general, theoretical ones.
The pursuit of fitness is usually undertaken through the practice of exercise and is considered beneficial because it enables the practice of more and more varied physical activities by an otherwise average human being. In their almost ceaseless quest for variety, challenge and the avoidance of boredom, humans are able to take great comfort in greater ability to pursue things they may never actually achieve3. Curiously, the frustration and boredom inherent in the pursuit of fitness4 is regarded as a natural coincidental of the pursuit. To those who do not seek fitness for any specialised purpose, however, this coincidental is often considered enough to prevent the pursuit.
Good health is a by-product of physical fitness which is also emphasised by those who seek or recommend it as a worthwhile goal of exercise. The effects of a well-rounded state of physical fitness on aspects of bodily function as diverse as metabolism and body fat to immune function and cardiovascular capacity are almost unexceptionally beneficial. The exceptions5 apply mostly to exercise (or over-exercise) itself, rather than the state of fitness which exercise is undertaken to achieve.
There are very few, if any, acknowledged poor health consequences of physical fitness. Bad health may be a by-product of the pursuit of physical fitness, however, if it is undertaken in the wrong way, or for the wrong reasons. Negative consequences of the pursuit of physical fitness often have much to do with the definition of ‘fitness' that the fitness-seeker is pursuing. Fitness equated or confused with slenderness or weight loss, for example, can often manifest itself in the appearance and activities of people who others regard as models of health: supermodels being the obvious examples. Anorexia, bulemia and other psychological disorders are possible concomitants of the pursuit of physical fitness in this context. Exercise addiction is also a possible coincidental. Last, but not least, the tendency to compulsion of fitness-seekers to do things like exercise, semi-naked and sweating, in sub- zero temperatures or in rainy conditions, is a likely harbinger of infection and consequent poor health, and such problems are usually dependent on the level of obsession which encourages the fitness-seeker to pursue fitness.