Sister Madonna Buder didn’t start running until she was 47.

Catholic nuns have a rep for being tough, but none are steelier than Sister Madonna Buder (a.k.a. the "Iron Nun"). The 86-year-old star of Nike's recent "Unlimited Youth" ad campaign has done over 375 triathlons—more than 45 of them Ironmans (a 2.4-mile swim, 112-mile bike ride, and 26.2-mile run. . .back to back). Women's Health asked the Washingtonian how fitness keeps her going.

You didn't start running until you were 47—how'd that happen?

SMB: A priest I met in Oregon suggested I take it up to strengthen my body and my mind. Four years later, I got into triathlons, for the variety. Competing in races helps me feel connected to others, united with a common goal. And, of course, staying fit and healthy means I can be of service to others longer.

Take us through your training schedule.

SMB: Like most people these days, I live a nonstop kind of existence, so most of my training is functional—I run to church in the morning, or bike to the jail, where I read scripture to inmates. You just have to squeeze it in. I can put in seven miles a day just going about my activities. Having competed for more than 33 years, I'm lucky to still be able to move.

How long will you keep competing?

SMB: My last competition was the Triathlon World Championships in Cozumel, in September. This year, we'll see; I plan only one day at a time. My grandmother taught me that. She used to say, "The past is dead and gone, never to return. The future is not the future when it gets here. So all you're responsible for is the present moment, and the future will take care of itself."