Originally Posted by whitetrashwarmblood
I was originally taught to post off the inside diagonal, but when I got into 4H and went to clinics the teachers told us to post off the outside diagonal. So does it really matter? Or what?
It only matters in classes like English pleasure and hunter type classes and in the US.
The is no correct diagonal in dressage and as mentioned earlier, posting on either diagonal is often done outside of the US. The reason I give to use the inside hind leg is on a advanced horse the the rider (assuming they are advanced enough and should be riding this level horse) following the natural rhythm of the post will have their inside leg is in the best postion for driving when the inner hind leg in its phase of support after its forward advance, so just as it touches the ground. This means the influence of the inner driving leg will impart a greater force and that hind leg acting on that force will push off with greater impulsion. This will now stimulate the outer hind leg to reach more aggressively forward in its swing.
So why do we want to influence the outer hind to swing more vigorously... This should become appearant in an arena with more close cramped quarters where turns ( not sharp ones) are commonplace. And that is because the outer hind leg MUST travel a greater distance on any turn than the inner hind leg. The rider's outside leg at the same time should act mainly as a support for the inner hind leg and requires less of a driving influence. So what happens is that the horse's outside leg is relieved of the load bearing and therefore becomes easier to swing farther forward to cover the greater distance it has to go.
Summery...The Europeans (mostly) are looking for better engagement.