By Tara Haelle
TUESDAY, Dec. 8, 2015 (HealthDay News) -- About half of young teens' daily physical activity occurs at school, but it accounts for just a fraction of their time there, according to a new study.
"We knew that schools were a major source of physical activity for kids. But, we were surprised that kids spent only 4.8 percent of their time at school physically active, the lowest of all locations," said study lead author Jordan Carlson, director of community-engaged health research at Children's Mercy Hospital in Kansas City.
Besides helping to prevent obesity and chronic diseases, physical activity has benefits for bone health, brain development, academic achievement, on-task behavior and mental health, Carlson added.
"Kids have a natural instinct to move around, and schools can support this by providing more opportunities for students to be active, such as by incorporating physical activity into the classroom," he added.
The study also found that walking to school added an extra 15 to 20 minutes of overall physical activity to children's days. Yet the proportion of kids who walk to school has dropped from 40 percent a few decades ago to 15 percent today, Carlson said.
Building schools closer to students' homes, improving pedestrian safety, and utilizing drop-off zones when the distance to school is too far "could have meaningful impacts on their overall physical activity and health," Carlson said.
The findings were published online Dec. 8 in the journal Pediatrics.
The researchers measured how much moderate to vigorous physical activity nearly 550 teens received daily by outfitting them with a GPS tracker and an accelerometer for an average of seven days.
The group of teens ranged in age from 12 to 16 and was diverse in terms of gender, ethnicity, family income and neighborhood type (easily walkable or not). They lived in either the Seattle or Baltimore-Washington, D.C. metropolitan areas.
The teens spent about 42 percent of their waking time at school and a little more than a quarter of their time at home. They also spent about 13 percent of their time in their neighborhoods and 14 percent of their time elsewhere.
Overall, the study found they spent an average of 39 minutes a day engaged in moderate to vigorous physical activity -- significantly less than the 60 minutes recommended for healthy development and obesity prevention.
On school days, just over half of this activity time occurred at school, the study found.
When averaged across a full week including weekends, teens got about 42 percent of their total physical activity while at school. They got about 10 percent of their total physical activity each week in their neighborhood or around their school, the study found.
Despite declining budgets, it's important that schools not neglect the value of physical education, said Dr. Jennifer Beck, associate director of sports medicine at the Orthopaedic Institute for Children in Los Angeles.
This is especially true at a time when obesity in children has swelled along with increases in diabetes, high blood pressure, high cholesterol and malnutrition in U.S. children, she added.
"The most important implication coming out of this study is that we as a society -- including parents, educators, health care providers and government officials -- need to do more to promote a healthy, active lifestyle among our at-risk adolescents," Beck said. However, she cautioned that this is a complex topic and said readers "should take care in drawing specific, concrete conclusions from the data."
Still, studies have shown that kids learn better when they have time for physical activity, "even at the expense of decreased study time for academic subjects," Beck said.
The current findings also reveal how much teens' lives have changed since decades past, before computers and multimedia sources were fixtures in the home, said Dr. Danelle Fisher. Fisher is vice chair of pediatrics at Providence Saint John's Health Center in Santa Monica, Calif.
"Kids rode bikes and walked to school or friends' houses," Fisher said. "Parents and kids have more structured activities today, which include lots of programmed extracurricular activities, and teens spend less free time around home."
For kids to get enough physical activity, changes need to occur at home and at school, Carlson said. Schools need well-trained physical education teachers, recess for younger kids, classroom physical activity and play before and after school, he said. Parents can also limit their children's screen time and advocate locally for more pedestrian-friendly neighborhoods, he added.