A successful foundation for any horse in Classical Riding can only be acheived after perfecting the shoulder-in. This is a lateral movement that results in proper straightening of the horse, promotes freedom in the shoulders, suppleness and most importantly the proper bending of the hocks. The proper bending of the hocks occurs over time and allows more weight to be carried on the hind quarters for future advanced high level movements with collection such as Piaffe and Passage.
The problem today with many dressage enthusiasts, is the degree of unnatural bend that is executed in the lateral movements. Over bending the horse while doing the shoulder-in will create a canceling out of the benefit of working the shoulder-in when the horse shortens his stride behind to compensate for his discomfort at being overbent. When over bent the horse is forced to shorten his stride, his inside hind and inside fore legs will not reach forward over the step of those of the outside. The exercise, done over time in this exaggerated position will not allow the horse to benefit from the increase in strength to the hocks when done correctly and gradually.
The improper bending and lateral work done will result in lameness in the hind quarters that have not been properly developed. Patience must be exercised along with regular proper execution of the shoulder-in, so the horse will become proficient at his own pace, avoiding injury and promoting pleasure in the horse as he or she performs this important movement in Classical Training.
The proper execution of the shoulder-in is mandatory to moving forward to each gradually more collected movement in the high school in Classical Training.
Source: Podhajsky, Alois, Die Klassische Rietkunst The Complete Training of Horse and Rider In The Principles of Classical Horsemanship, Wilshire Book Company, 1967, p.133-136.
