Lip Syncing

[Mathew]

Hi,
Every performance done by an established singer on X Factor seems to be lip syncing. Is there some sort of rule which means they can't sing live, or what? Just seems rather odd that they don't sing live when it's so noticeable that they're miming.

Thanks,
Matt

[Conservative,]

They can't strain their voice obvs.

[Judas]

They can't strain their voice obvs.

WHAT LOL? no...

i dont think all of them have done. usher didnt, but then again he didnt sing half of his performance lol did rihanna? as far as i dont know there isnt a rule that says so but in the past they havent, e.g. last year lady gaga and black eyed peas definitely didnt. i dont think shayne ward did on sunday either cos he had this HUGEEE bum note, and katy perry didnt either cos she went off in a few bits as well.