In the United States today, we are starting to see more and more of a problem with children who are overweight. Doctors and even the President's wife are trying to do something about it. Not only are they recommending healthier foods, but they also recommend that children exercise daily. They suggest that children go outside and do things instead of sitting in front of the TV. They have indicated 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. They also recommend that children do exercises that strengthen the bones and muscles. There are lots of ways children can do this, primarily through running.

According to the passage, which exercise causes the heart to beat faster?