“Not all is as it appears.”
It’s been called the “aspirin of equitation”. Those who chase dressage honors talk about it like it’s just an everyday chore. Cow-horse trainers talk of two trackin’. In any event it is the lateral movement used in horse training that develops permeability, elasticity, and collection in the horse’s body. This is because in a good shoulders-in at the walk, the horse learns to reach up under the mass of his body and bear weight on his inside hind leg, bending the joints of that leg, then pushing off. The crouching movement required for for high school or for cow work comes from this movement. It is how the horse is induced to shift his weight and balance to his hind legs.
One day a friend asked about shoulders-in while I was starting to work with a client’s horse. The first question was “How do you keep him from banging his inside foreleg into his outside shin when crossing over as he steps?” I began the explanation by saying that the movement requires a certain amount of bend and a certain amount of angle off the wall. The bend comes from the rider’s seat bone pressing down on the inside of the horse’s back. (“Inside” refers to the center of the arena. “Outside” refers to the wall or rail side of the horse.) The angle comes from the reins bringing the shoulders inward off the track, outside rein predominant, inside rein only enough to help with the bend.
Then my friend asked “Well, how is it that you sit to the inside? I thought you told me years ago that because the horse can’t actually bend its backbone in the middle, it rolls its spine to the outside. That ought to make you sit to the outside!” I rocked back on my heels. It was quiet for a while. Then an epiphany came to me.(It didn’t hurt!) I have so often had difficulty sitting into my right seat bone when attempting the right shoulder is in. I feel like I’m falling off the horse’s right side. Then it hit me. That’s because most horses have more resistance to bending to the right. Only when they develop the flexibility to roll the spine to the left, do they give you a “place for your right seat bone to sit”. How much easier all this would be if only we could converse with them! As it is, we patiently repeat the exercise until it starts to feel right, then quit for the day. We can always ask again tomorrow.