Researchers study the daily physical activity of hundreds of eight-year-olds, and find that the happiest kids are also the most active.

Children who regularly exercise are better equipped to handle stress, according to new research.

Scientists at the University of Helsinki in Finland were the first to explore the link between physical activity levels and stress hormone responses in children.

To do this, they studied the daily activity levels of 252 eight-year-olds using accelerometers, devices similar to pedometers that measure a person’s movements. They also took saliva samples to check for levels of cortisol, a hormone released when the body is under stress.

The children were then given tasks, including math assignments and speaking in front of others. After, their stress hormone levels were tested again.

Researchers found that children with the highest levels of physical activity also had the lowest levels of cortisol following stressful tasks, suggesting they were better equipped to handle anxiety.

“The findings suggest physical activity plays a role in mental health by buffering children from the effects of daily stressors, such as public speaking,” lead study author Silja Martikainen, MA, said in a press release.

Martikainen’s research was published in the Endocrine Society’s Journal of Clinical Endocrinology & Metabolism (JCEM).

Though researchers have linked physical activity with decreased stress levels, they’re still unsure what mechanism in the brain causes these changes. Unlocking that secret could be the key to creating effective medications for depression and anxiety.

Pediatric endocrinologist Henry Anhalt, DO, chair of the Endocrine Society’s Advocacy and Public Outreach Core Committee, said the Finnish research only scratches the surface of the effects exercise has on our mental health.

Anhalt called the study “an important foundation of discovery,” but acknowledged that more research is needed to determine why we feel better after exercising and how we can identify biological differences before and after exercise.

“That’s the million-dollar question,” Anhalt said in an interview with Healthline. “The only thing you can take away from [the research], as a parent, is that exercise is good. We know exercise is good for the body and the mind.”

This study is further proof of the importance of instilling positive, active behaviors in children.

Previous research on childhood stress has found that environmental factors, including stress, can affect the physical makeup of the brain and bring out mental illness in those with a genetic predisposition.

Along with the mental health benefits of regular activity, the physical benefits of exercise range from a decreased risk of chronic illness to better school performance.

Conversely, childhood obesity has been linked to higher rates of grade repetition, depression, allergies, and more.

While we may not know just why exercise makes us feel better, we know it does. If your child is acting a little stressed out or cranky, take him or her outside to run around for a bit. It’s good for both of you.