Why do drivers move their head forward when accelerating

[AudiLeon96]

Hi guys,
Never really understood this phenomenon but what else better to think about at midnight. As the title says, why is that when drivers accelerate (usually from standstill) they move/lean their heads forward into acceleration? I see this very often whether it be a 90hp polo cutting me up on a roundabout or a higher powered vehicle accelerating onto the slip road of a motorway. Anybody else noticed this and have an opinion? Quick search on Google gave no results

 

[DieselJake]

I've never noticed this but maybe it is to brace for the potential of their heads being thrown back (due to the extreme power of a 90bhp Polo )

 

[SootySport]

They are hanging onto the steering wheel due to extreme G forces exerted on their body. I also don't understand the way some people sit in a car, when you can adjust the seat and steering wheel hundreds of different ways.