Childhood in Western countries has seen a gradual elimination of physical effort and a corresponding decline in physical fitness. Car ownership does not oblige people to walk as much as previously, and people spend much more time on physically undemanding forms of recreation, as when 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.
Children have become more sedentary. A sedentary child expends 700 calories a day, compared to 1350 for an active child. Children on average 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 activities that would bring their heartbeat up to 140 per minute for 30 minutes a day. 60 minutes a day is the minimum required to improve one's health.