Sammy is 12yrs old. Ok now I'm just kind of taking a stab here because I'm not that experienced but. I think he is unbalanced when ridden faster then a walk. At first I thought it was just the barrelracer coming through but now I think about it he might actually be unbalanced. Whenever he trots he tends to rush (and try to break into a canter somtimes) and brace against your hands. I haven't cantered him in awhile because I am trying to get his trot good before I try again but when I did it was very fast and (cant think of the right word right now) uncontrolled.
Also I had a feel of his shoulder, back and legs today. He didn't respond to anything on his shoulders. The most he did when I felt his legs was turn around and watched me but he didn't seem bothered. When I checked his back the first time he sunk away at a particular spot. I tried a second and third time just to be sure but he didn't react again it was just the first time.
Oh also he does it with all four feet but is probably a bit worse with his front feet.