Here's a great stretch for your piriformis muscle! The piriformis muscle is part of the lateral rotators of the hip. The piriformis laterally rotates the leg with hip extension and abducts the femur with hip flexion. Abduction of the flexed thigh is important in the action of walking because it shifts the body weight to the opposite side of the foot being lifted, which keeps us from falling. When the piriformis is very tight or spasmed, it can put pressure on the sciatic nerve and cause sciatica (pain down the leg).