The piriformis is a small muscle that is beneath the buttocks. If the hamstrings or quadriceps muscles of the thigh are weak, the piriformis support these muscles in bending and extending movements.
Pain right below the buttock area after sitting too long.
The piriformis is often strained through overuse and is the result of muscle imbalances in the leg. When the piriformis goes into spasm, it can feel as if there is a lump in the buttock area.