I've only seen the information about the cracked rib in an interviews released yesterday where Charlie says he cracked his rib "on the cheerleading episode. So the rest of the competition I was duct-taping my ribs up and taking lots of painkillers. I was definitely hampered. It was about a month sleeping on one side."…

Something I don't see mentioned in this article or comments: apparently Charlie was suffering from a cracked rib (incurred during the cheerleading challenge) and was in quite a bit of pain. With that information, it starts to make sense why he couldn't move around much during the lip sync.