The psoas (pronounced so-as) are the deep core muscles that link the upper and lower girdles of the body. They lie below the surface muscles of the body and are the ‘missing-link’ riders must learn to use in order to feel their horses’ movement and to follow the directions of their riding instructors.
You cannot see the psoas and they do not appear on charts of the surface muscles of the body. They are located deep in the abdomen, on both sides of the lower spinal vertebrae.
We do not usually think of these muscles because the functions they perform are done in conjunction with one or more of the body’s surface muscles. This is probably the reason the riding world does not look further than the surface muscles at the front and back of the body when determining how riders stabilize themselves on their horses.
The psoas muscles are the bridges between the upper body and the legs. They are the only muscles that directly link the spine to the legs. The psoas attach directly from the lower spine to the top of the inner thighs at the lesser trochanter of the femur.
Balanced flexion of the psoas muscles enables riders to tone the inside of their upper thighs and to allow the movement of their horses with their pelvises. The psoas enable riders to influence their horses with their seats and legs.
By mastering the use of these muscles, riders will be able to maintain self-carriage, both on and off the horse. Riders will be able to develop self-carriage and have independent seats.