But they can't do it either, that's the thing. Dancing hard and singing at the same time is impossible. each time one of their fans/stans showed me a performance to justify their claim, there have been two alternatives:
1- The live part part when they were walking or standing still. Each time the dancing came, the prerecorded track (playback, in other words) was switched on.
2- Everything was prerecorded, with some shout here and there.
PS/ I don't know if you're a singer but if you are, try to do it. Try singing and dancing your ass off, you'll see a huge change, for the worse, in your vocals. If you see a popstar doing that and there's absolutely not the slightest variation in her singing then you can be 100% sure that she's lip syncing.
The only time Gaga really used pre-recorded vocals was for Judas, other than that most of it is her singing live. A lot of singers use back track. The issue is when a singer lips a whole performance in an attempt to make it seem like the singer is actually attempting an effort. And of course there's always a difference when you sing and dance, your diaphragm isn't just gonna stand in place while you move