On the Forehand and the Thoracic Sling

Horses do not have a collar bone. Their ribcage is suspended by a group of muscles that work together to form what’s called the thoracic sling. If these muscles are not engaged, the ribcage will drop and the horse will be on the forehand, which means that they have a lot of weight on their front legs. The chest appears dropped, the horse will appear to be going downhill, and the back appears quite hollow. If the horse is on the forehand and with a dropped ribcage, then when a rider sits on a horse, the amount of weight carried on the forehand increases further, and the back will hollow even more. To carry a rider healthily, the horse needs to engage the thoracic sling and lift the forehand, bringing more weight onto the hind legs. This prevents the back from hollowing, and helps the horse to move more freely, because the muscles of the back are able to move correctly when the back is lifted. 

When the horse is taught to lift the forehand through slow walk work, the footfalls become light and elegant. The horse takes big, free, smooth steps. The walk feels really smooth and glidey, and the horse becomes incredibly receptive to the aids. They are easy to manoeuvre and become more willing and forward going. The horse becomes more eager to trot and canter and the trot and canter also feel smoother and easier to ride.