I actually don’t think they do. If you look at this classic video:
Robert Förstemann puts out .021 KWH powering a 700 Watt toaster, this means he lasted for 1.8 minutes.
(.021 Kilo Watt Hour) (1000 Watt/1 Kilo Watt) (1/700Watt) ( 60 Minutes/1 Hour) = 1.8 Minutes
While I don’t want to say it is impossible to do 1000 watts for 2 minutes, I think it would have to be a person with the perfect storm of huge size, huge anaerobic and huge aerobic engine.