NOT LONG AFTER I MET MY BOYFRIEND, I put a tracking device on him. I didn't quite mean to do that. What I did, really, was follow him on Strava, the GPS-powered social app that maps workouts. I was 23 and a nonexerciser who stayed fit with a precarious regimen of genetics. My new boyfriend was a talented triathlete whose values included pain tolerance. So I bought running shoes and joined Strava.
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