The psoas is an important ribbon-shaped muscle that runs from your lower lumbar spine (the lower back) to the top of the femur (thigh bone), explains Jim White, R.D.N., A.C.S.M. Ex-P, owner of Jim ...

Specifically, a muscle called the psoas. It’s buried deep inside your core, linking your lumbar spine to your legs, playing a key role in everyday movement. If this muscle becomes tight or weak ...