Should You Post the Outside or Inside Diagonal? Or… what you may really be asking… What’s a Diagonal?

If you have ever watched young competitors at a horse show you have probably heard parents and coaches on the sidelines whispering to their rider “wrong diagonal” or “change your diagonal!” Similarly, many riders both young and old are taught diagonals and then reminded often of the importance of rising with the outside shoulder (at least in the United States) when trotting.

While some may be given the logic, or at least the argument, behind always riding on the outside diagonal – many riders, myself included, were first taught to ride the outside diagonal because “that’s what you need to do in the horse show.” But why do we really ride the outside diagonal when posting the trot? Why do some argue that it is better to post the inside diagonal? Or what some of you may really be asking: What is a diagonal?

I decided to do a bit of research to find better answers to these questions and then do my best to present them to you in the clearest way possible.
First, let’s clarify what a diagonal actually is. The trot is a two beat gait, meaning that the horse’s legs move in diagonal pairs so that there are two legs on the ground, bearing weight and pushing off, while two legs are suspended. The front right and left hind move together, as do the left front and right hind. This creates the up and down movement that we feel when we are in the saddle. If a horse is stronger in one diagonal, you may find yourself always posting to that diagonal, as their will be a stronger “push” propelling you out of the saddle and into the rhythm of that diagonal pair of legs. “Outside” or “inside” diagonal refers to the outside or inside of a circle or the arena you are working in. Although you want to be able to feel which diagonal you are on, if you are posting the trot and you glance down at your horse’s shoulder, you will notice that you are coming up in your post as one of your horse’s shoulders is swinging forward. If you are rising as the outside shoulder moves forward then you are on the outside diagonal or vice versa.

Posting to one diagonal does put more work on that set of the horse’s muscle, so it is important to change diagonals. If you post to a specific diagonal in the arena this is easy because you change it every time you change directions. However, if you are outside the arena, perhaps out for a hack or trail ride, it is also important to regularly switch your diagonal in order to work the horse’s muscles more evenly.

Now to the discussion of outside vs. inside. When a horse turns or is on a circle, the outside hind leg moves more – it has to swing around and take a bigger step. However, the inside leg bears more weight from the horse and has to push harder to propel the horse’s body through the turn. The logic behind the outside diagonal is that by posting in rhythm with the inside hind leg, we free the outside hind to move more freely. In addition to this, it is generally easier for the rider to use their leg during the seated moments of posting, and since they are seated when the hind leg is still on the ground, ready to push off, then the rider is better able to influence that hind leg.

The logic of the inside diagonal says that we need to post in rhythm to the outside hind leg in order to free the inside hind leg, allowing it to push off better, with less weight, and come further under the horse’s body. In areas of Europe it is standard to post the inside diagonal, while in the United States, we all learn to post the outside.

I can understand the arguments for both and it can be an interesting topic for debate, however, I believe that it is important not to become too fixated with diagonals, especially when still learning to feel the horse’s movement. Instead, I feel that it is most important to be aware if your horse always “throws” you on a particular diagonal, because this is a clue that he may be stronger and more pushy on one diagonal and could use work to become more even in his strength and movement. Also, we need to remember to be aware of our diagonals so that we are changing them periodically, again working both diagonals evenly.
In the video below, I put two different colored boots on one of my horses to show the diagonal pairs of legs and what posting to a specific diagonal looks like. I also show a change of diagonal, plus put things in slow motion so you can really see the mechanics of the trot.

Which diagonal do you post? Do you have a reason other than those I mentioned? Share it!

I’ll see you in the comments! Callie