I have never been thin by running standards. If I'm in the low 170s for 5' 10″ I am doing good. When I PR'd at Boston in 2002 I did get below 165. I got down to 158 once and ran terrible. I like to be around the 172 range, but have run good ultras at 180. It was never a real big deal to me if I was running a lot. I have to run to my ideal weight, trying to diet never had a good effect. A lot of it has to do with my natural big hips and thighs.