I’m going to discuss the rhomboids and trapezius muscles as one, since it is very difficult to differentiate them by touch or by performance. The rhomboid and trapezius muscles cover the withers and go up the neck to the poll. They are the muscles that allow the neck to arch. When contracted, they can cause a ewe neck to develop. This muscle is also attached to the shoulder blade and pulls it forward and up in motion. Healthy muscles in this area will allow a horse to travel in an uphill frame comfortable and naturally.
Many horses have a dip in front of their withers. That is an indication of a tight rhomboid. Since this tightness can take up to a year to change, I always show owners how to massage the area so it can be done on a daily basis.
Tightness in the trapezius can cause a hollow back. It is important to release the tension since the horse will often develop hind end problems to compensate for the discomfort. Everything is connected! When the rhomboid/trapezius area is contracted, I almost always find trouble in the muscles of the shoulder. I will discuss those muscles (spinatus) in another post.