Working conditions in modern industrial societies are generally characterized by a gradual elimination of physical effort and a corresponding decline in physical fitness. Car ownership removes the former obligation of walking, and people spend much more time on physically undemanding forms of recreation, such as watching television or playing computer games. Children fail to exercise adequately for these and two additional reasons: unsuitable play facilities and parents' fear of letting their children out alone.
Lack of exercise is causing a deterioration in health, particularly among the middle-aged in developed countries. Many complaints about ill-health, pains, and the malfunctioning of various organs may be related to a subnormally functioning muscular system. Weak muscles often cause more passive structures of the body (joints, ligaments, and connective tissue) to be overloaded. Increasing mortality rates are associated with a higher incidence of cardiovascular disease and with a lower level of physical fitness.
In 1997, 59% of American adult women and 49% of adult American men took little or no exercise; 50% of young people aged 12 to 21 were not regularly active. The Centers for Disease Control and Prevention said that only 25.4 percent of adults met government recommendations for physical activity in 1998 -- virtually unchanged from the beginning of the decade -- and that almost 30 percent reported no physical activity at all.
Children have become more sedentary. They expend 500 calories less per day than they did 10 years ago; only one tenth as many children walk or cycle to school as did then. In a study to measure children's energy output, researchers found that virtually no children engaged in actitivities that would bring their heartbeat up to 140 per minute for 30 minutes a day.
The number of cars and the number of televisions owned by European households doubled in the 20 years up to 1997, which ties directly to a drop in exercise.
The medical profession does not have reliable information about the degree of benefit from physical exercise; some say mild exercise improves health, others say only vigorous exercise prolongs life.