It’s been an open secret for years that Britney Spears does not actually sing at her live concerts. She is lip-synching to the pre-recorded tracks of her albums. The excuse usually given is that due to the high-energy dance routines that she performs while she “sings”, she would be too out of breath to give a good vocal performance.
But it sure doesn’t sound like she’s all that breathless to me in this video clip of a live performance which includes an audio isolation capture of her headset mic:
It’s pretty awful. It’s obvious that she isn’t even trying to sing, but it does make one wonder just how much effort has to go into making her studio work passable. You have my full dispensation to watch only as much of the clip as you are able, you will not be quizzed on this later.

My ears are crying, and Britney is caterwauling all the way to the bank.