Katy has literally never. Even when she should have, she is a true artist to the end.
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Gaga may have not totally lip synced, but we have that audio from Judas on SNL. We know how much those backing tracks were helping her.
Anybody who has performed at the Macy's Thanksgiving Day Parade has.
Because unlike the good sis Katy, Gaga was dancing. Also she had that heavy ass outfit on his little ass frame, of course she was going to get tired. I suggest you lookup her audio vocals at the 2013 VMAs and see how much backing track help her when she keeps it simple.
Gaga her backing tracks are so loud she might as well (and has come extremely close in the past). Oh and that one time at TMB in Manchester where for whatever reason certain songs were 100%.