It depends on a lot of things. In the winter I'm on a 166m track, and the G-forces there are extreme. Stuff breaks - mostly seats, spokes, maybe seat posts, clamps. First time I road the thing my legs were fine, but my neck was a wreck from trying to hold my head up. My butt wasn't much better. For training I switched over to an old seat just because it has gel padding. I even seem some bikes with brooks leather.