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 actitivities 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.