It’s become a common sight in sun-drenched Seattle parks: outdoorsy types balancing on what looks like a wide, flat tightrope strung between two carefully padded trees. It’s called “slacklining,” and Adam Burtle, 32, is Seattle’s authority on the sport, which originated with rock climbers in Yosemite in the 1980s and is gaining fans and practitioners locally. The slackline is a 1- or 2-inch-wide piece of nylon webbing (such as that used in climbing gear) with a bit of spring to it, which is why slackliners often bounce as they walk. Burtle’s website, nwslackline.org, connects aficionados across the city and offers pointers. Having taught people as young as 5 and as old as 70, Burtle advises beginners to give in to their most basic balancing instincts (such as those used for riding a bike). “What you’re doing in slacklining is unconscious,” Burtle says. “It goes from being really hard to being magically easy. You have a superpower, you are walking on this wire in the air!” When he isn’t defying gravity, Burtle focuses on his first love: health-based humanitarian work and activism, as a volunteer for the Red Cross and a University of Washington student preparing to apply for med school. He hopes to practice medicine in underserved areas someday, and plans to bring a slackline wherever he goes.