05/19/2025
The posterior pectoral, often called the ascending pectoral or caudal deep pectoral, is the largest of the pectorals, and is the only one that comes into contact with the girth. It originates on the sternum and inserts on the humerus. When the horse is in locomotion, the muscle is responsible for pulling the trunk towards the front leg, and when the horse is static, the muscle draws the leg in towards the body. It is a major shoulder stabilizing muscle, and helps to suspend the trunk.
Simple muscle tightness here is a very common cause of shortened strides. If the posterior pectoral is tight, the leg can’t extend forward fully, so forward motion is inhibited.
A common cause of muscle soreness or dysfunction here is poor girthing. If a girth is too narrow or too tight, it can inhibit this muscle’s activity, and it may also cause decreased blood flow, damage and pain in this muscle, all of which will affect the horse's movement.
If your horse is ‘girthy,’ this is an important muscle to check: stand at the horse’s shoulder and run your hand along the lower portion of the rib cage (right behing the elbow). **THIS MAY BE SENSITIVE, SO BE PREPARED FOR YOUR HORSE TO MOVE AWAY OR REACT** If the muscle is relaxed, this area will feel flat and soft. If it’s tight or in spasm you’ll feel a knot—a lump in the shape of a small hot dog, across the muscle (perpendicular to the ground).
Now it’s time to call your horse’s massage therapist!
Here’s another single session before and after of a horse that had significant adhesions, and was very painful on palpation of his posterior pectorals. By the end of the session he welcomed touch to the area, and the tension was released. ✨