Muscle knots in the Iliocostalis Lumborum are located in the lower back. These muscle knots often feel like a deep, aching pain in the lower back that can radiate into the buttocks. These muscle knots can make the area hypersensitive to touch and may cause stiffness or discomfort when bending, twisting, or sitting for long periods. You may describe the pain as a dull burn or a tight band running along the spine, especially after lifting or prolonged inactivity.