By Amy Norton
MONDAY, Sept. 26, 2016 (HealthDay News) -- Over 90 percent of U.S. high school students don't get enough exercise to stay fit and healthy, and the pattern persists after they graduate, a new study finds.
The researchers followed students at 44 high schools for four years, and found that only 9 percent met current exercise recommendations throughout that time. For the most part, those habits held steady after high school -- though college students were more active than non-students.
There was also some variation among college kids, the study found: Those who lived on campus exercised more than those who lived at home.
It's not clear why those students were more active. They might have been more involved in sports, for example, or simply walked more -- running from classes to dorms and other campus buildings, said lead researcher Kaigang Li.
"The walkability of your environment is important," said Li, an assistant professor of health and exercise science at Colorado State University, in Fort Collins.
The study is far from the first to show that most U.S. teenagers need to move more.
According to Peter Katzmarzyk, a professor at Louisiana State University's Pennington Biomedical Research Center, in Baton Rouge, "This study really confirms the low levels of physical activity in adolescents, which appear to be maintained over time as they transition into young adulthood."
A strength of this study, he said, is that it objectively measured teens' activity levels: They wore devices called accelerometers, which tracked how much they moved over the course of a week.
Katzmarzyk, who was not involved in the study, conducts research on child exercise patterns, obesity and health.
The U.S. Centers for Disease Control and Prevention has long recommended that children and teenagers get at least an hour of physical activity each day. That mainly means exercise that boosts the heart rate, such as running. But, kids should also try some strength-building activities -- for example, push-ups or lifting light weights.
Studies have shown that few young people are heeding that advice, however, according to the CDC.
That may be partly related to a lack of physical education in schools: Only 29 percent of U.S. high school students have gym class every day, the CDC says.
The evidence from this new research and other studies makes a good argument for more physical education, according to Katzmarzyk.
"Any way that we can increase physical activity levels in adolescence might translate into maintaining higher levels of physical activity in young adulthood," he said. "So physical education in high school is certainly an important outlet for this."
Still, Li said, there are probably numerous reasons for teenagers' low exercise levels.
He noted that in elementary school, most U.S. kids do get enough physical activity. But there is a steep drop-off after that. According to Li, that could be related to many factors -- including heavier homework loads starting in middle school, and more time on cellphones and computers.
The new findings are based on 561 students who were followed for four years, starting in 10th grade. Over 90 percent fell short of getting an hour of exercise each day over the study period, Li's team found.
What's more, the study participants' activity levels typically declined in the year after high school graduation -- especially if they did not go to college. Those who went to a four-year college got a little more exercise, particularly if they lived on campus.
According to Li, that suggests that college life -- possibly by giving students access to gyms and other facilities -- helps young people be more active.
Still, he said, colleges can do a better job of promoting exercise. The same goes for communities, so that all young people have opportunities to move every day, he added.
"Communities could create more walkable environments, public parks, bike trails, or low-cost or free exercise programs," Li said.
However, gyms and bike paths "aren't enough." Kids also need to learn, early on, how to build healthy habits into their day, he stressed.
"Especially as kids become independent," Li said, "it's important that they have the skills to manage their time and make good choices."
The study findings were published online Sept. 26 in the journal Pediatrics.