Tracing Longissimus Thoracis (51)
to its lower attachment again brings us to an area where you can’t tell the players without a scorecard. Most people assume they can feel the back of their pelvic bones and the sacrum in between if they probe for them.; this idea is further enhanced by the fact that these muscle attachments can become hard as bone. And if you think something is a bone, you'll not bother to stroke, or pulse across it, thereby leaving some important muscles locked in spasm.
Quadratus Lumborum to the 3rd Lumbar (14)
and Gluteus Medius (15)
cover the posterior crest of the pelvic bone with thick muscle. The crest of the pelvic bone at the front of the body is not so covered, and thus can be felt.
Multifidus to the 3rd Lumbar (13)
and Longissimus Thoracis (51) form the hard mass that is felt from the surface of the body, (51) covers the tuberosity at the rear of the crest of the pelvic bones. Note that when (51) is traversing the space between the ribs and pelvis, the Longissimus Lumborum (52) which attaches to the lumbar vertebrae is just lateral to (51).
51 doesn't miss its last opportunity to irritate one more muscle, 13 (multifidus). This final victim creates a problem which is the most devastating of them all. 13 rests against the 4th lumbar nerve, which can cause deep pain at the base of the spine and is responsible for those instances when someone gets locked in the bent-over position. Pain in this nerve reflexively causes 14 to contract and draw over to the side the 3rd lumbar vertebra (to which both 13 and 14 are attached), so as to lift 13 off the entrapped nerve. This leads to the skewed torso pattern.
The reflexively contracted 14 (QL) generates a great amount of lactic acid due to the constantly induced state of contraction, and so irritates itself into even further contraction. It is the most common site of low back pain
and is ultimately responsible for causing the disc protrusion that gets the blame. Quadratus Lumborum reflexly recruits Psoas (26)
into spasm in order to counterbalance part of the resulting pull. An imbalance between 14 and 26 causes the vertebra to rotate.