You’ve probably heard the complaints since you were a kid yourself – children aren’t getting enough exercise. Now there are numbers behind this notion.

According to a new report by the U.S. Centers for Disease Control and Prevention, more than half of adolescents aged 12 to 15 are considered physically unfit.

The authors of the report tested more than 600 young teenagers on treadmills to measure cardiorespiratory fitness, a measure of how well the heart and lungs can move blood to supply muscles during exercise.

They found that just half of all boys and only a third of all girls in the study met the bare minimum threshold of being called “fit.” Taken as a whole, this meant that only 42 percent of kids were fit. In 2000, by comparison, this figure was 52 percent – lackluster for sure, but still a majority.

Not surprisingly, overweight and obese children were less fit than those who had a healthy weight; only 30 percent of overweight children and 20 percent of obese passed the minimum standards to be called fit. But even so, only 54 percent of children with normal weight – barely half – had adequate levels of cardiorespiratory fitness.

Dr. Jaime Gahche, the lead author of the report, said the solution is clear – children simply need to get up and move.

“Children should spend at least 60 minutes daily,” Gahche said, “mostly doing aerobic exercise, like walking, running, participating in team sports or martial arts.”

Keith Ayoob, director of nutrition at the Albert Einstein College of Medicine’s Rose R. Kennedy Clinic, agreed that the findings are a clear signal that American children need more physical activity.

“We have got to make sure that no kid is left on his behind,” said Ayoob, who was not involved with the study.

Competing for kids’ time with these activities, of course, is a growing proportion of the day devoted to computers, tablets and other forms of screen time.

“Kids come home after school nowadays and don’t even leave the house,” said Dr. Dyan Hes, clinical assistant professor of pediatrics at Weill Cornell Medical College, who was also not involved with the study. “Especially teenage girls – they chat, they text, they go online. It’s really a sad state.”

It’s Official: Most American Kids Are Physically Unfit – ABC News