Shoulder-In is the “Vitamin B” for Balance. – “8”.

“The shoulder-in prepares a horse to be put on its haunches, because with each step taken in this posture it carries the inside hind leg forwards under the belly and brings it over to the outside hind leg, which it can do only by lowering the haunch: it is thus always on one haunch in one direction, and on the other haunch in the other direction, and learns in consequence to bend its hocks under itself; this is what is called being on the haunches.”
François Robichon de La Guérinièr

 

To have your horse ready for shoulder-in under saddle he needs to :
Go forward freely.
Turn a full turn on the forehand.
Turn a full turn on the haunches.
Lateral flexion to both rein.
Leg yielding to both sides.

From the Ground
“Standing beside the horse’s shoulder–let’s say the left shoulder–lightly hook the first two fingers of your left hand through the ring of the snaffle. Hold a whip in your right hand about the same level as the point of the horse’s shoulder, with the shaft pointing toward the horse’s tail. Grasp the right rein in your right hand with the length of rein–crossed over in front of the withers–adjusted so that you can control the degree of bend. With your left hand holding the snaffle ring draw the horse’s head and neck toward yourself and start him moving forward with a tap or two of the whip. You, of course, walk along beside the horse. In this way you can see for yourself how he moves his feet”.

 

The shoulder-in is the most basic and most used of the forward-traveling lateral maneuvers in Cowboy Dressage. This is a maneuver performed on three tracks.
If you are riding a shoulder-in to the left, the right front foot moves to the left to travel in the same track as the left hind foot, while the left front foot moves to the left to travel in its own track.
In the shoulder-in, the horse bend into the direction of travel. Visualization of this maneuver is the key to successfully riding a shoulder-in.

By traveling in a straight line with bend through the front of the body, the horse’s outside or leading shoulder has to reach forward while the inside shoulder has to take a slightly shorter step. In order to keep the horse traveling in cadence in a straight line, the inside hind leg is required to step deeper to compensate for the shorter step of the inside front leg. This strengthens the hip flexors of the pelvis, which are important muscles of balance.
The horse’s balance shifts from the evenly distributed four-beat walk on two tracks to carrying more weight on the diagonal pair that is traveling on the same track. In this way, you can isolate and strengthen the muscles on the diagonal pair, one side at a time. If the horse moves from three tracks to four tracks in the shoulder-in, you lose some of this strengthening of the diagonal in the maneuver as each leg then carries even weight. In much of the lateral work that shifts the horse’s weight from two tracks to three tracks, you can see this same strengthening phenomenon of the diagonal pair. Holding the horse to just three tracks can be more difficult than moving the horse onto four separate tracks because he is then evenly carrying his weight on all four legs again.
Probably the easiest way to teach the shoulder-in to both the horse and the rider is by using 10-meter bend. When riding forward out of a 10-meter circle, hold slight bend through the horse’s shoulders, head, and neck while releasing bend in the hindquarters. Weight the horse’s diagonal pair of legs by driving the energy for- ward from the inside hind leg to the outside front leg. Maintain contact with the inside leg to prevent the horse drifting to the inside of the maneuver. Your outside leg helps maintain propulsion in the maneuver. Think about concentrating the balance in your body, and therefore, in the horse’s body, on that middle track, driving the energy forward through the movement.
When creating a shoulder-in from a straight line, continue to ride straight and forward, making slight contact with your inside leg to hold the horse on a straight line. Then, ask for bend by making a slight contact with the inside rein and “pushing” the horse’s outside shoulder over with the outside rein.
In the beginning, many horses will want to fall to the inside, following the bend of the head and neck. You can correct the horse by supporting with the inside rein and shifting his weight to his outside hind leg. Another technique is to drive the horse forward and release the bend, while straightening the horse back to two tracks. Then ask again for the shoulder to step just one track over to the inside. Once the horse has softened and is moving on three distinct tracks, release the horse to a free walk on a straight line. As the horse is learning to balance through this maneuver, it is important not to ask for too much at one time.

 

Shoulder-In gave birth to a baby named Shoulder-Fore.

Shoulder-fore is a lateral movement which encourages your horse to take more weight onto his hind legs and step actively underneath his body. Although it’s not a required movement in any Cowboy Dressage tests it’s a really useful flat work exercise to do with your horse. It’s great for developing straightness and improving balance.