Shoulder-in is the father of the advanced lateral dressage movements. It does many wonderful things for your horse. Here are just some of them:
What Does Shoulder-In Look Like?
The horse flexes to the inside and bends around your inside leg. His forehand comes in 30 degrees off the wall so he's on three tracks. At this angle, his inside hind leg lines up behind his outside foreleg. Sometimes in competition the judge likes to see a hoof's width more than three tracks, but don't bring the forehand in more than that, or you'll lose the bend.
What Are the Aids?
If you're doing left shoulder-in, the aids are:
1. Put your weight on your left seat bone.
2. Keep your left leg on the girth for bend and to ask for engagement of the inside hind leg. v 3. Place your right leg behind the girth to prevent the hindquarters from swinging out.
4. Use your left rein to create a +1 flexion at the poll.
5. Keep your right rein steady and supporting to prevent too much bend in the neck.
6. Keep both hands low and equidistant from your body as you move them to the left. Move them to the left enough to place the outside front leg in front of the inside hind leg. Use your inside rein as an opening rein. Bring your outside hand very close to the withers, but never let that hand cross over the withers.
What's the Sequence of Aids?
Always ask for bend before you ask for angle. The formula for the advanced lateral exercises is Bend + Sideways = Engagement. It's not Sideways + Bend = Engagement.)
Marks of a Good Shoulder-In
The quality of the shoulder-in really comes down to bend. You know your horse is bending if his hindquarters are in exactly the same position (i.e., parallel to the wall) in shoulder-in as they are when you're just riding straight down the track. If his hindquarters swing out at an angle to the wall, you're just doing a leg yield in a shoulder-in position.