Technically, you still can. Problems with neck and back are most common. But they aren't nearly as common as running injuries. I recall reading that even experienced serious long distance runners average one major leg/foot injury every two years (the kind of injury that will prevent you from running for a month or two.)

Here's a short table to help check the proper bicycle fit
http://www.aafp.org/afp/2001/0515/p2...010515p2007-t3