Muscle knots in the Iliocostalis Thoracis Caudal (lower) Portion of the are typically located in the mid-to-lower back along the muscle mass that runs parallel to the spine and attaches to the lower ribs. This muscle often refers pain both upwards and downwards along the back, and importantly, can cause a confusing referred pain pattern on the front of the body in the side of the torso, chest, or abdomen.