Essentially, an "acceleration" is a surprise increase in speed--doesn't
really matter how fast you start and how fast you end up--just a command that
causes the horse to suddenly tuck his butt and reach out. A little burst,
then come back to the slower trot and wait for a while, then another sudden
burst. 10 strides, 20 strides, really doesn't matter as long as the horse has
to change his shape to accelerate quickly.
This will lead to the horse driving from behind--and trying to get his front
feet the hell out of the way. And that will mean the the hind feet will begin
to impact the ground slightly before the fore feet do--positive dissociation.
ti