Yielding the Chest (from pages 145-146 of Lessons in Lightness: The Art of Educating the Horse)
The purpose of engagement, whether in the forward gaits or in rein-back, is to rebalance the horse to lighten the front end. The phrase “yielding the chest” describes the ultimate lightening of the shoulder as the old masters envisioned it.
Some horses, through breeding or natural athleticism, will naturally―or through discovery―lift the chest to increase engagement. Other horses can be taught the yield once they have sufficient strength to hold the additional change in balance.
Keep in mind that horses can lighten to the aids and perform well in every aspect of this training program without ever discovering this additional lift and its resulting lightness. Yielding the chest is more-than-normal lightening of the shoulder. The idea of lifting the chest higher is a lofty, but attainable, goal that can distinguish the top equine performers.
The rider cannot command the chest to lift without compromising the back nor can the rider pull the horse’s chest higher. The horse must find the yield himself. Rein-back provides the format in which many horses can learn. The power of the back and haunch, as evidenced in exaggerated lowering and tilting of the pelvis in rein-back, stimulates the horse’s ability to maximize lift.
Typically, horse with a naturally flat body carriage or those ridden in the lower position over an extended period of time (which is sometimes necessary in order for the rider to access the horse’s back) will want to remain balanced forward. By raising the rein, the rider can coax a response from the horse. Yielding the chest requires the horse to “think outside the box”―he has never been given this aid before. But if he obeys and has sufficient strength, his chest should lift as his neck rises with the rein. Only release the rein when the chest lifts higher. Any elevation will be felt under the rider’s seat. Though this is only a slight change in overall balance, the result will be a very distinct sense of lightness. The horse’s front end will seem to float above the ground.
While rein-back places the horse in the best position to find lift, the practice of using rein to lift the chest can be applied at any time, in any exercise. Just be aware that the yield upward will come in very small increments. Acknowledge each measure of lift that the horse offers with an immediate release of the rein. This acknowledgment encourages the horse to find more lift (to the degree that his strength allows). For some horses yielding the chest can become a game of who can release faster. This level of communication defines the ultimate bond between horse and rider and brings body language to a truly profound level.