Before I had a child, I only occasionally set foot in the many parks in our neighborhood. Now I spend so much time in them that I can tell you about every swing set, picnic table and unfenced patch of grass within a two-mile radius. Also the location and cleanliness quotient of every park restroom.

A study published Wednesday finds my own relationship with parks is part of a larger trend: Urban parks in the U.S. are largely geared toward the young, with far less appeal for adults, especially older ones. And that leaves on the table a big opportunity to use parks as a way to increase physical activity.

"You'd think that seniors would be retired and would have more time" to go to the park, but "they're not using the parks very much," says Deborah Cohen, a senior natural scientist at RAND and lead author of the study, which was published in the American Journal of Preventive Medicine.

Adults ages 60 and up made up only 4 percent of park-goers, even though they're 20 percent of the population.

While the potential health benefits of public parks have been cataloged, there's been less research on describing the nation's park infrastructure. Researchers at RAND Corp. wanted to get an idea of what's currently on the ground in cities with a population of more than 100,000. So they sent data collectors into 174 parks in 25 major cities, asking them to describe the facilities and conditions, and the demographics of users during a typical week during the spring or summer of 2014.

Parks, of course, varied from neighborhood to neighborhood. But looking across the entire survey sample, almost all had lawns and play areas. About half had outdoor basketball courts and baseball fields. But just 29 percent had a walking loop, and the percentage of parks with a dedicated exercise area or fitness zone was in the single digits.

Those basketball courts and swing sets are also the ones more likely to be used by kids and teens, so it's not a surprise that 38 percent of park users were children and 13 percent teens, though those demographic groups represent 20 percent and 7 percent of the U.S. population.

Breaking that down by gender, boys accounted for 60 percent of the time children spent on moderate to vigorous physical activity in the parks. Among teens, that figure was 68 percent.

Cohen says that disparity may be explained by a greater participation in park-based team sports like T-ball and basketball by males. Overall, 57 percent of park users were male.

There were also disparities in use by neighborhood income, with parks in high-poverty areas used less than in low-poverty ones, even though facilities were similar.

Parks represent an efficient, cost-effective way to improve public health, researchers say. "If you give people convenient, safe access to park space where they can do physical activity, they're more likely to do it," says Ross Brownson, a professor of epidemiology at Washington University in St. Louis. Parks also may offer a mental health benefit by exposing people to nature.

So how to attract more users? Provide more facilities aimed at older folks and people of all ages, for one. For example, localities are increasingly promoting the intergenerational use of parks by adding walking trails around playgrounds and ball fields, so parents can keep an eye on their kids while getting some exercise for themselves, says Andrew Mowen, a professor of recreation, park and tourism management at Penn State University.

The study found that more supervised activities like classes or organized sports and more marketing via banners and signs were associated with more hours of moderate to vigorous physical exercise in the parks. Brownson said it's important to target that to what's popular in a given community. "If it's soccer, animals, hunting and fishing, scenic beauty," park administrators need to tailor programs and outreach accordingly, he says.

Katherine Hobson is a freelance health and science writer based in Brooklyn, N.Y. She's on Twitter:@katherinehobson

Copyright 2021 NPR. To see more, visit https://www.npr.org.