Adolescents less physically active than adults post-ACL injury, MSU research finds

April 18, 2022

After fully recovering from an ACL injury, adolescents are significantly less physically active than adults, according to research led by Michigan State University scholars.

The research, published in the Orthopaedic Journal of Sports Medicine, discovered 83% of adults were physically active after being cleared for unrestricted physical activity post-anterior cruciate ligament surgery—but only 9% of adolescents were.

Students walking on campus of MSU.
Photo courtesy of MSU Communication and Brand Strategy.

“What was shocking about this study was not that adolescents and adults had different physical activity levels, but the magnitude of difference shocked us,” said Chris Kuenze, associate professor in the Department of Kinesiology and lead author on the study.

According to researchers, this is the first study that investigates the role of participant age in PA after reconstructive surgery. And while the findings merit further study, researchers say they come with some worry about the future: Physical activity patterns developed early in life are predictive of patterns in adulthood. In other words, if adolescents are not physically active now, they are also not likely to be when they reach adulthood.

Chris Kuenze

The data examined individuals ages 13-35 and who had ACL reconstruction surgery 6-12 months prior. All had been cleared by a physician for physical activity (PA) before being enrolled in the study. They wore a PA monitoring device on their hip for seven days at all waking hours, except during water-based activities such as swimming or showering.

Adults (18-35 in this study), on average, participated in physical activity for 16 more minutes and took 2,212 more steps per day than the adolescents (ages 13-17) in the study.

A healthy human

“Often, we think of ACL recovery in terms of returning to sport. But we need to think beyond that,” said Assistant Professor Shelby Baez, who contributed to the study. “This is about overall health and well-being.”

The U.S. Department of Health and Human Services PA guidelines suggest adolescents should exercise at least 60 minutes per day with aerobic, muscle-strengthening or bone-strengthening exercise. Adults are encouraged to do at least 150 minutes (about 2.5 hours) minutes of moderate-intensity aerobic activity in addition to at least two opportunities per week of muscle-strengthening activity. The guidelines, published in 2018, indicate that although there has been improvement in PA among American adults, “only 26% of men, 19% of women and 20% of adolescents report sufficient activity to meet the relevant aerobic and muscle-strengthening guidelines.”

The scholars stress both groups could use some improvement in their numbers and their PA, but that only 9% of adolescents met their guidelines was notable, if not concerning.

Shelby Baez stands on campus with a background of green foliage. She wears a white button down and a gray cardigan over top. Her dark hair is shoulder-length and curly.
Shelby Baez

Kuenze and fellow scholars—which include Kinesiology students (Katherine Collins) and fellow Kinesiology faculty (Baez, Ashley Triplett, Matthew Harkey), among other collaborators—say this is an “interesting snapshot” of physical activity, and that it has generated new questions and ideas for researchers.

“We need to look for more ways to promote physical activity,” said Baez. “Why do some people engage in healthy lifestyles, whereas others do not? How can we shift mindsets to improve health for everyone?”

Next steps

But first, scholars—such as those at MSU—need to discover what is limiting physical activity in the first place. Kuenze, for example, is working on interviewing patients (particularly adolescents) about what they may feel is limiting their ability to be more physically active. Already, he can imagine some of the limitations he may hear about. People may be afraid to re-injure themselves, but there are also social factors to consider.

“If there is a challenge about accessing sport, that may be one reason we’re seeing these numbers,” he said. “In addition, kids like to do sports and physical activity because it’s fun, they’re with friends. If their friends aren’t engaged in sports, then physical activity becomes less fun and they may turn to other, less physically active things to engage in social contexts, like video games.”