I was watching a video clip of a horse I know practicing a dressage test. During the extended trot he traveled very wide behind but as soon as he went back to the working trot this went away. And it did not show up anywhere else that I could see. This horse was not particularly relaxed in his movements. My first thought was he moved this way to not over reach (he is barefoot). I am trying to make sense of it and would appreciate any thoughts. It is just a curiosity to me.
Yes, Kindred, that's exactly why: he goes wide behind so as to avoid stepping on his front heels.
Horses that are ridden on the forehand, as we know this one must be, have one of two options to avoid hurting themselves by stepping on the fore heels: they can either go crooked, i.e. displace the hindquarter a half-width either left or right, so that one hindlimb lands wide and the other lands in between the forefeet; or else spread both hind limbs as this horse does, to go wide behind.
How we know that the horse you observed is travelling on the forehand is that if he were travelling in proper back-to-front balance, the contacting forefoot would have already been lifted before the arrival of the hind foot that might step on it. When horses are on the forehand, the excess weight that is upon the forehand acts to hold the forefeet down into contact with the ground longer. The more the horse is overweighted in front, the longer the forefeet will be held down.
That you report that the horse appeared to be tense merely corroborates what we already knew from his "solving" the problem by going wide behind. My bet would be that if you look again at the video, you will also discover that the animal drops its back just behind the withers, has a peak over the top of its croup, and a broken neck.
The bottom line for our students here is never to let any of this pattern develop. The key is to stop paying any attention to dressage teachers who tell you to "push the horse forward" or that your horse is "not forward enough." All green horses are way too much "forward" as it is, even in those relatively rare instances when they seem to be sluggish or lazy. They are too much FORWARD and not enough UPWARD, and the whole object of higher-level training is to convert them from "forward" movers to "upward" movers. "Pushing" a horse that is already out of back-to-front balance -- that is to say, because he moves forward but not upward -- merely knocks him further off balance and makes it, moreover, even more difficult to get his feet underneath himself so that he can move "upward."
There is an enormous difference in the meaning of "forward" and the meaning of "not putting forth enough energy" or "not responding to the aids." It is the latter factor especially that is usually the problem, and it cannot be solved by "pushing" in any form. Cheers -- Dr. Deb