When your ass/legs/abs/arms are on fire, glaring at the instructor will not benefit you.
Working harder will.
The science behind the lactic acid burn is shocking: Lactic acid is actually fuel for your muscles, not a sign to stop.
According to an article in the New York Times, muscle cells convert glucose or glycogen (i.e., carbs) to lactic acid. The lactic acid is taken up and used as a fuel by mitochondria, the energy factories in muscle cells.
Training hard in brief spurts doubles this process, something sports trainers have known for years but science has only recently come to acknowledge.
So go ahead and glare all you want. But double down on those pliés if you know what’s good for you.