02/10/2026
Everybody knows about diagonals, right? However, not long ago I was talking with a riding instructor who had shown a fair amount including as a member of a college equestrian team. The subject of diagonals came up, and I could tell she didn't understand why we rise when posting the trot in a bend on the forward reach of the outside diagonal.
I explained why and her response was that no one had ever taught her. Now she is teaching diagonals to the next generation without giving a reason why we rise on the outside diagonal except that it's what judges want.
The reason why we rise on the outside diagonal is based in the fact that in a bend the inside diagonal is shorter than the outside diagonal. In the image below the right diagonal is shown as being shorter than the left diagonal. We want to rise on the outside diagonal to free up the horse's outside reach that is longer than the inside reach that is somewhat "compressed" in the bend.
Additionally, by rising on the outside diagonal, when we straighten our knees, our body moves somewhat forward as well as upward. This lightens and evens the stride as a result of our body mass being slightly forward. When we sit the trot with a trained horse the push is more from their hind than any pull forward with their shoulders. Therefore, when we post the push from the hind becomes less intense and freer.
Lastly, there is another reason for posting on one diagonal instead of the other, and it is when the horse is going straight at the trot and when the diagonals are of equal length. Can you guess why?
The lengths of US Cavalry mounted marches were limited by regulations. A standard distance was 25 miles per day and for a forced march the limit was 75 miles. If the Cavalry Troopers posted always on one diagonal, their horses would develop their muscles unevenly. To prevent this the Troop was required to periodically change diagonals all together on command. The Troop leader would count off a number of strides, I have read 50, and then tell the troop to change. I know very little about endurance riding, but I suspect that they follow this same principle as the Army did.
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