wow
It's called drive phase. You keep your head down and accelerate further. Allows you to go further in the 7 seconds you have before alactic energy declines and you have to slow down.
"Head down" should be an *effect* of the acceleration--it's not intrinsically a cause of it.
For most, the ideal probably is to have the head neutrally in line with the neck/torso: neither artificially bowed down, nor prematurely looking up at the finish. The greater the acceleration, the more of the center of gravity will be ahead of the supporting foot ==> the greater the body lean (and the more the head will be "down").
Yes, the head is more or less in line with the torso, but bringing the head UP sooner than necessary causes a premature end to acceleration, while keeping it down prolongs it. You keep the body angles forward and the head down for as long as you have the strength (and this is the limiting factor) to continue to accelerate--and keeping the head down helps keep the body angled forward. John Smith uses the airplane analogy here about coming up gradually. As soon as you become vertical, you are in the maximum velocity and speed maintenance phases and acceleration ceases.
As long as Bolt is in vaguely good shape and half-caring, Powell will never beat him again.
that's what your girlfriend looks like when she is leaning over, diving head first on my pipe...she looks like a crackaddict