In the United States today, we are starting to see more and more of a problem with children who are overweight. Doctors are trying to do something about it. They recommend healthier foods and encourage children to get daily exercise. They also recommend that children go outside and do things instead of sitting in front of the TV. They have suggested that children exercise at least an hour a day by jumping rope, cycling, or anything else that makes their heart beat faster. This kind of exercise is known as aerobic exercise. Something else they recommend is for children to do exercises that strengthen the bones and muscles. There are lots of ways children can do this. One way is running.

Which of the following details in the above passage explains what doctors want children to do?