The piriformis muscle lies deep in the buttocks and rotates the leg outward. When the muscle shortens or contracts the sciatic nerve, which lies underneath the muscle, may be compressed or irritated and causes pain, tingling, and numbness in the buttocks and along the sciatic nerve (down the back of the thigh). Piriformis syndrome can be caused by overuse of the muscle while sitting (biking, rowing), running, flat feet or by having tight adductor muscles (inside your thigh). It is common to see this condition in runners who do not properly stretch.
Treatment for Piriformis Syndrome will include stretching and strengthening as well as massage therapy.