Shoulder-in ‒ the undisputed, most important fundamental movement in dressage and English riding. It allows you to be able to move the shoulders where you want and when you want, as well as the added benefit of engaging the inside hind leg, creating collection.
But how do you know if it is shoulder-in, the collecting exercise, or leg yield, the suppling exercise? They can seem the same, and they can look the same when you are in the saddle ‒ but they are definitely not the same!
For the intermediate rider learning to ride the lateral movements (like leg yield, shoulder-in and haunches-in) it is less important to know the difference or even feel the difference. The most important thing is to understand how to move the shoulders to the inside track. This is also fundamentally different than pushing the haunches out, which may result in the same angle, but is definitely not the same. Remember, it is called “shoulder-in” not “haunches out.”
The act of turning the shoulders to the inside is the secret to activating and engaging the inside hind leg. Pushing the haunches out is the secret to asking the horse to drop the inside hip and step under the body, resulting in suppleness.
Lets talk leg yield. The act of pushing the horse sideways, away from the inside leg, with some flexion in the jowl, is a suppling exercise. All types of leg yields do this: turn on the forehand, spiral in/spiral out, leg yield from centre line to wall, or wall to centre line, and nose-to-rail leg yield. All of these leg yields have the same aids, all of them develop suppleness and connect the horse to the outside rein as a precursor to bending around the inside leg.
It is the act of turning the shoulders that creates bend in the body, and it is the bend in the body that requires the horse to engage the inside hind leg to trot a shorter distance on an inside curve, as the outside hind leg has a longer distance on an outside curve.
TIP: Watch horses’ legs/footfalls on a 10m and 8m circle. Do the horses’ legs track true, inside hind leg to inside front leg, and outside hind leg to outside front leg? If they are avoiding the bend and thus avoiding engagement of the inside hind leg, then the horse will cheat by going wide behind, or by popping the shoulders out, and then the footfalls will not be in alignment. If the track is true, then the horse is bending in the body!
By the way, if the horse is kicking the boards during shoulder-in or starting/ending a circle, then you are definitely losing your outside hind leg!
Now you know the theory about what is different and why you need to know the difference. Now we can answer HOW can you tell if you are in shoulder-in and if your angle is correct.
Shoulder-in is a three-track movement where the shoulders are to the inside track of the hind legs. (More about the imaginary person later.)
The aids for shoulder-in are the same for turning. You have inside flexion, inside leg to outside rein while turning with the outside rein as you come out of the corner or a 10m circle. It is a simple turning aid like you do to turn a 10m circle. Its the half-halt that is the secret to maintaining the shoulder in.
TIP: the bend and arc of the shoulder-in for second and third level is 10m. (The place on a 10m circle where the front legs leave the track is the same arc as the shoulder in.) The inside leg to outside rein half-halt will let the horse know to stay in the curve with the shoulders off the track rather than continuing onto another 10m circle.
If you can do the shoulder-in but always end up off the wall or drifting in, the issue is the half-halt. Practice 10m circles to shoulder-in, with a transition to walk at the end of the 10m circle and beginning of the shoulder in, or walk when your horse leaves the track too far. If the issue is you cannot get the shoulders off the track, then you need to image leaving the wall before you half-halt ‒ again walking where half-halt is needed ‒ with the neck straighter than you think.
Now that you have an idea of shoulder-in, how do you know what is a good angle? I find this trick works for pretty much every horse!
When you are in shoulder-in, imagine you have someone walking/jogging beside your horse’s outside shoulder. Your horse’s shoulders are to the inside, so there is a space right beside the outside shoulder for someone. Take care not to step on or bump into that ‘person’. You are also supporting the outside hind leg so that it doesn’t kick the wall or bump into the ‘person’ if you were to turn back onto a circle.