In shoulder-in, you ride your horse at a constant angle of approximately 30 degrees to the track with a slight but uniform poll-to-tail bend around your inside leg.

He moves away from the direction in which he is bent. Because of the bend and angle, his inside fore passes and crosses in front of his outside fore and his inside hind steps forward under his body, following his outside fore. If you were to stand in front of him, you would see three tracks: inside fore; outside fore and, directly behind it, inside hind; outside hind. You sit slightly more on your inside seat bone (less because you reposition yourself than because your horse lowers his inside hip with each step). You can feel that he’s giving you nice contact on the outside rein—just enough that you can easily give on your inside rein and he doesn’t lose balance, bend or angle.

In Germany we call shoulder-in “The mother exercise of all lateral work.” For the first time in your horse’s training, he not only has to ­accept your outside half-halting aids, bend around your inside aids and stay supple in his poll, he has to travel rhythmically forward with his haunches not aligned with, and following in the track of, his forehand. His inside hind leg accepts more weight and his inside hip lowers, which allows his forehand to lighten. Shoulder-in is a challenge, but once your horse masters it, he’ll be stronger and more supple, and far more likely to find the other lateral movements—travers (haunches-in), renvers (haunches-out) and half-pass—fairly easy.

Shoulder-in Prerequisites

• A mastery of leg-yield. Your horse completely understands and willingly responds to your sideways- and forward-driving aids while staying straight through his body.
• A degree of collection. He moves forward on the bit with an energetic impulsion, his neck somewhat raised and arched, and the whole structure of his haunches (hip, stifle and hocks) well-engaged. His steps are a bit shorter than in working trot, not ­because you are resisting or holding him with your hand, but because your seat and legs are driving him forward into an alternately “restraining” and allowing hand that encourages him to engage and bring his hind legs farther underneath his body. However, if your horse tends to get lazy or stuck, I don’t see any fault in occasionally riding shoulder-in at more of a working trot, as long as he stays balanced and supple and the trot doesn’t get so fast or forward that the movement becomes choppy. In fact, I often purposely ride working trot to get more cadence.
• The ability to do a shoulder-fore. This is all about what we call “relative straightness.” Left to his own devices, your horse will align his outside hind and outside fore against the rail. But because his haunches are wider than his shoulders, that brings his inside hind just a little more into the arena than his inside fore so he’s relatively crooked. When you position his inside shoulder in front of his ­inside hip, he’s straight because his ­inside hind is following in the track of the inside fore.
• Throughness or Dürchlassigkeit. There’s a free and easy flow of energy and aids from back to front and from front to back as a result of his musculature being connected, supple, elastic and unblocked.
• Self-carriage. He is supple in his poll and appears to work almost on his own without relying on you to hold him together. And this is important! If he’s not carrying himself, shoulder-in—all lateral work, for that matter—can actually have a negative effect on his training and development. When you ask him for shoulder-in’s flexion, bend and angle, he’ll just lose his balance and lean on your hands, become resistant or fall out over his outside shoulder. For the best way to check that your horse is in self-carriage, see Photos 1 and 2 at right.
• Balance on an 8- or 10-meter circle. On a light contact, your horse bends evenly from poll to tail ­according to the circular track without any loss of ­tempo or quality of movement.

Get Started Training Tip: Use the bend and aids on an 8- or 10-meter circle. They are so closely related to the bend and aids in shoulder-in that they comfortably and logically set up your horse to begin the movement and help him restore those qualities if he gets into trouble during the movement. Come through the short end of the arena in collected trot and in the corner, circle 8 or 10 meters. (If slowing things down and walking helps you figure out the aids and your horse understand them, by all means walk a few times.) Anytime you feel your horse slow down or struggle during shoulder-in, slightly relax your inside leg and circle to restore bend, balance and impulsion. At the end of the long side, complete the shoulder-in by again softening your inside bending leg aid and allowing your horse to bring his shoulders back to the rail in front of his haunches. It is good schooling to finish with a circle. It keeps you from cutting the corner and allows you to realign your horse’s body for a correct corner.

Training Tip: Shoulder-in isn’t an end unto itself—it is a gymnasticizing exercise intended to improve your horse’s suppleness and balance. So ask for just a “baby” bend and angle at first and only increase bend, angle and flexion in gradual, doable stages. Asking for too much too soon will just have a negative effect. Your horse will lose his balance or the quality of the trot, fall out over his outside shoulder or try to hold himself up by leaning on your hands.

Once your horse is confidently performing a shoulder-in this way, eliminate the circle but use the same aids to ask for shoulder-in after coming through the corner. When that’s going well, try shoulder-in on the centerline where you don’t have the support of the rail. As long as you ride with mirrors or have a friend who can be eyes on the ground, it is a great check on your aids and your horse’s response to ride shoulder-in left, straighten for several strides, then ride shoulder-in right. See if you can keep his haunches on the centerline and not swinging or falling through your inside or outside aids. Make sure the exercise isn’t hectic, with you flip-flopping three strides here, three strides there and your horse flinging from side-to-side. It must be a very predictable, balanced, smooth change from left flexion, bend and angle, to straight, to right flexion, bend and ­angle. When you can do that and keep your horse’s haunches on the centerline, you can be pretty sure that the two of you have mastered shoulder-in!

Training Tip: If your horse starts to get stuck and dull to your aids, his muscles could be getting tired. Anytime you start to feel that you’re working harder than you should to get results, give his muscles a break. Change direction or do circles or serpentines. And don’t forget that it is always a good idea to take a short walk break.

Shoulder-in Problem Solving

• Check the photos below for two of the most common problems—too much neck bend and too wide an angle—along with trouble-shooting solutions for each. Other problems you can encounter riding shoulder-in …
• Your horse follows his shoulders and falls in off the rail. If he’s like most horses, he doesn’t like to bend, or the idea is so new to him that he interprets your shoulder-in aids as a request for him to turn. Correct him by riding straight down the quarterline and leg-yielding to the rail. At the moment you arrive, sit a little more on your inside seat bone and use your inside leg at the girth to bend him as if for a shoulder-in. Do shoulder-in for just a few strides down the rail and then straighten him and trot straight ahead. Repeat the exercise a few more times and he should begin to understand that he can do both: bring his shoulders in and leave his haunches on the rail.
• Your horse loses forward energy. ­Return to the more familiar bend of a 20-meter circle and alternate collected trot with a more forward trot so your horse learns to go forward on a curved line. Chances are, he’ll be better able to go forward while staying bent and going sideways in shoulder-in. Or try an exercise that I often teach. It not only ­restores a horse’s forward thinking, it ­increases teamwork and agility. Come through the short side on the right hand, say, and ride slightly forward on a shallow diagonal line from M to A. When you arrive at the quarterline, apply the aids for shoulder-in right and continue down the quarterline until you feel your horse slowing down. Straighten, ride a few strides toward A again, then reapply your aids for shoulder-in.
• Your horse rushes. This is often ­because he doesn’t like to bend or go sideways. First make sure that he’s strong and balanced enough to be doing shoulder-in. If so, ride a 10- or 15-meter circle, using half-halts to control his tempo, and then, with that control, go back into the shoulder-in, but with gentle, careful aids and a slower tempo.