The shoulder in is the first collection exercise in dressage. It helps to engage the horse’s haunches so the hind legs push and bend more. It helps to lift the horse’s forehand so the horse is stronger, more flexible, and more maneuverable. The shoulder in is used to prepare the horse for transitions and for lateral movements such as half pass. It can help avert a shy. It serves to correct crookedness and weakness behind. Because the shoulder in serves such a myriad of purposes, it has been called "aspirin for horses."

Basically, the horse is bent in the arc of a circle but is traveling straight down the long side of the arena. His hindquarter stay on the track of the wall and his shoulders, head and neck come in, so he is advancing down the wall, parallel to the wall with his shoulders slightly to the "inside" of the arena, thus the name, shoulder-in.

Tracks

When the horse travels perfectly straight, he is on one track like a rail road track, with the left legs forming one rail and the right legs forming the other. You can see the tracks as you watch the horse’s feet hit the ground. A horse on a large circle may be bending along the circle line but still be on only one track. In shoulder in, the horse begins two track work. Two tracking is a kind of general term for any lateral work the horse does. Let’s say the horse is going right. In shoulder in, the horse might have so much bend and flexion that he goes on 3 rails or tracks. In shoulder in, the outside hind leg goes on a track by itself. The inside hind leg bends, engages, and comes so far under that it steps into the same track as the outside shoulder. They form one track. The inside front leg steps on its own track. This gives us a 3 track shoulder in.

Degrees

If you’re mathmatically minded, it might help to think of the angle the horse forms with the wall in shoulder in. The more he brings his shoulders in, the greater the angle he forms with the wall. In an ideal shoulder in, the horse forms an angle of about 30 degrees with the wall. If the angle gets to be any more than 45 degrees, it is too wide, the horse will fall on four tracks and will be in leg yield instead of shoulder in. In leg yield, you lose the collective powers of shoulder in.

O’Clock

Yet another way to determine the horse’s angle on the wall is to think of the wall like the big hand pointed at 12:00, and the horse’s head and shoulder’s like the little hand. In shoulder in right, the forehand should face between 1:00 and 2:00 o’clock and in shoulder in left, the forehand should face between 10:00 and 11:00.

What happens physically for the rider

Weight, leg, rein

The rider’s aids, in the beginning, are the same as on a circle. Keep your weight to the inside by stretching your inside heel and leg down and your inside shoulder back and up. Your inside leg is active at the girth to ask the horse’s inside hind leg to step further under. Your outside leg is back (and either passive or active) to keep the haunches from falling out. Remember the movement is shoulder-in, not haunches out. The inside rein corrects the inside bend, but then rewards. The outside rein stays steady to keep the outside shoulder from falling out.

Another way you can think about the same thing is to keep your hips parallel with the horse’s hips, your shoulders parallel with this shoulders and your chin lined up with his poll. Be careful not to tip or lean in an effort to put the horse in position—you’ll only throw him more out of position.

10 meter circle

The 10 meter circle has the same bend and flexion as the shoulder in. Bend refers to the horse’s longitudinal bend along the circle line. Flexion is the folding of the poll when the horse comes on the bit. If the horse does 10 meter circles without losing too much balance or tempo, he is ready for a few steps of shoulder fore or shoulder in.

Shoulder fore

The shoulder fore is a slight shoulder in. If the 10 meter circle has the same bend and flexion as the shoulder in, the 15 meter circle has the same bend and flexion as the shoulder fore. If you think of the shoulder in like a gymnastic, stretching exercise, you can think about it like learning to do the splits. You don’t get all the way down in one day, it takes weeks. Shoulder fore is like the beginning stretch for the splits. The horse is not in a complete 30 degree angle with the wall. He is just beginning to get the idea of bringing his shoulders off the track.

Counter shoulder fore

In counter shoulder in, the horse is bent toward the wall rather than toward the inside of the arena. Some people call it a "shoulder out" and others call it a leg yield toward the wall. The wall helps some horses (and riders) stay steadier in their angles. The counter shoulder fore on the horse’s stiff side can help him to listen more to the rider’s leg since the wall stops him from escaping the aids. It can keep the horse from falling out over the shoulder as well. To begin counter shoulder fore, ride your horse through a corner. About half way through the second corner, shave the corner line a little. Change your aids and the bend toward the wall. Proceed at an angle as you come out of the corner. The horse will bring his shouders slightly to the outside of the track, (toward the wall) and his haunches will be slightly to the inside. The counter shoulder in is different and easier than haunches in because of the direction of the bend. It is simply a shoulder fore done toward the wall rather than away from the wall. Again, just ask for three or four steps, the bring the horse’s shoulders back to the track. Straighten the horse as a reward.

It is fine to introduce any new movement in walk. Lateral movements help the horse maintain the purity of the walk, so you probably won’t hurt his walk at all. It is also fine to allow the horse to slow his tempo a little when he is beginning a new movement. By slowing the tempo, allowing the horse to slow his walk a little, you allow him time to think about what he is doing and learning. You also give the green or clumsy horse time to think about where to put his legs. Because the horse is beginning to cross his legs over each other in lateral work, it is easy for him to interfere. If he is hurried too much, he could interfere with himself by hitting any of his legs against the other. Since this hurts, he can learn to associate pain with the shoulder in. So, let it be slow until the horse figures it out. It’s always easy to add "forward."

In the beginning, it is no sin if the horse comes off the bit when learning a new movement. A young or green horse has enough to worry about just trying to get his legs placed correctly. A rider just learning the movement has enough to worry about also, and should ride the legs of the horse and not the horse’s head. The shoulder in itself will help the horse come round. After the movement is mastered, it’s always easy to add "round" and "through."

One of the best ways to start the shoulder in or shoulder fore is to come out of the corner, maintain the bend, and ask the horse to continue down the long side for just a few steps in shoulder in. The corner line is the same bend and flexion as a 10 meter circle line, so the horse is "set up" for shoulder in, if you ride your corners accurately. If the horse performs a few steps, you can straighten him again by taking his shoulders back to the track or by bringing his haunches off the wall on the same track as the shoulders. I like to do both when introducing the movement so the horse doesn’t learn to fall back to the wall nor does he learn to dive in to the middle of the arena.

Another good way to introduce shoulder in is to do a 10 meter circle on the track. As you return to the track, ask the horse to take 2 more steps on another 10 meter circle. This brings his shoulders off the track in the correct angle. Then, continue down the long side by asking his hind legs to stay on the track with your inside leg and his shoulders to remain inside with your outside rein.

Falling In

In the beginning, the most common flaw is for the horse just to turn into the inside of the arena. If the horse’s haunches come off the track, immediately circle 10 meters, and return to shoulder in as you reach the track. Don’t shilly shally. To drift around in a big circle rewards the horse for coming off the track. Complete your circle and get right back to the business of shoulder in. Use your time on the circle to review your aids. Always feel free to throw in a 10 meter circle any time something goes amiss in shoulder in.

Neck in (over-bent in neck)

This is a rider error, not a horse error. If you use too much inside rein to pull the head in, you can actually overbend the horse in the neck and throw the shoulders out! So, be sure you soften very often with the inside rein. This allows the horse to step under with the inside hind and to get his angle and engagement. You want to keep the shoulders from falling out with your outside rein, which closes like a door to keep the neck straight and the shoulders following the head. You can even think "neck rein" with your outside rein.

Shoulder in is the foundation for all of the higher level movements. To paraphrase Kyra Kyrklund, if you can’t control the forehand of the horse, you can’t control the hindquarters. Control the feet, control the horse.