My wife had a similar experience. Being the last child, she was just never pushed to do any activities in school, and had really never participated in any physical activities. When we got married, I set a goal to run a marathon, and she thought that was the funniest joke she'd ever heard. Funny story, turns out she was a natural at running, and handily beat me a few years later in our first half marathon, even though I played sports since I was a kid.