...something it wasn't designed for? I'm talking about something like riding on trails or up steep inclines or anything like that. I was biking with friends as a teen once and was on a singlespeed. We decided that it would be a good idea to hit one of the trails that happened to be full of rough terrain and an uphill climb. I didn't get hurt or anything, but let's just say that I was convinced my legs were never going to function again after that.