Author: Bryan Lang, PT, DPT, MHA, CSCS, Cert.DN: Doctor of Physical Therapy, Business Owner, Associate Professor, and Blog Contributor. Explores common client questions, helps find solutions for every day functional health concerns, and interprets difficult theories in healthcare rehabilitation. Committed to life-long learning and education. Learn more about Bryan on Google+.
There are SO many muscles that affect our hips and low back that I wanted to walk through them and discuss how I choose to treat this complex system. This is an article with a lot of technical terms. If you are not familiar with something or have more questions, contact me directly.
1. Start with the deep core muscles
Muscles we’re talking about:
1. Pelvic Floor
5. The Diaphragm
Question: Can you isolate these core muscles?
Yes and no. I believe if you can relax/inhibit the surrounding larger muscles, you can at least quiet down the ambient noise. Also, the law of parsimony states that we recruit our smallest muscles first in order to be efficient with our energy. As long as the exercises are very small and focused on these muscles in particular, I believe you can at least provide training that influences the deep core muscles more specifically than global exercising.
Remember, just because a general exercise could recruit a stronger contraction of the deep core muscles, it doesn’t mean they aren’t being overburdened by the larger and more superficial layers of spinal stabilizers. Sometimes you must relax the larger core stabilizers first before you can get proper activation of these deeper muscles during exercise/functional activity. We’ve already had great studies demonstrating that multifidus atrophy occurs in relation to low back pain, and even when pain is relieved, muscle bulk is not automatic. 
A Note on pelvic floor muscles:
They are real, they are important, and even if you don’t specialize in pelvic health PT, you need to learn how to address issues that do not require a referral to a pelvic health PT specialist. During an active straight leg, it was found by O’Sullivan that the pelvic floor descended up to 12 mm in patients who had SIJ pain.  There was minimal movement of the pelvic floor in control subjects without pain. That’s a really big difference! It’s like building a house -- if the foundation isn’t sound, the house will fall down no matter what you use to build it.
2. You absolutely MUST progress to the primary core stabilizers
Muscles we’re talking about:
We know that many of these muscles become excessively activated or turned on in patients with lumbopelvic pain. This is why starting with the deep core muscles and inhibiting these over-active muscles is crucial at first. Then, however, these muscles must be retrained to function properly because like-it-or-not, they’re always working.
It has been shown that the psoas major atrophies in the presence of low back pain and has altered recruitment patterns. 
The quadratus lumborum muscle, in appearance, looks like a guy wire and it attaches to every lumbar vertebrae, the rib cage and pelvis. With myoelectric evidence, it is active in virtually every loading mode (flex/extension and lateral side bending). It’s also active when you stand upright and compress the spine. 
Between the psoas major, the quadratus lumborum, and the deep layers of the longissimus and iliocostalis lumborum, you get a 3-way triangulation of forces to stabilize the spine. It’s like the ropes of a tent post.
In some individuals, these muscles will need to be strengthened (one or all), in others they will need to be stretched, and others will need these muscles inhibited in one form or another. However, if you don’t address them, you’re missing a big piece to the puzzle.
3. You can’t forget about the unsung heroes
Muscles we’re talking about:
If you’ve ever owned a business, you realize quickly that you can’t do everything, and if you try, you’re wasting time that can be spent making your business better. If you focus just on the core muscles (deep and primary), you’re going to miss the real heroes of lumbopelvic stabilization. These are the gluteus complex (maximus, medius, and minimus) and the latissimus dorsi.
The gluteus maximus is one of the more important stabilizers of the lumbopelvic system. It can tense the thoracolumbar fascia and the fascia lata through its distal attachment to the IT band. This all adds stiffness to the sacroiliac joint. In response to low back pain, the glutes become inhibited and the hamstring becomes dominant. 
Though the hamstrings can help stabilize the pelvis in sagittal plane movements, it’s critical to restore and ensure normal gluteal function in activities of daily living.
The latissimus dorsi (lats) also affect the thoracolumbar fascia but from the superficial aspect of it. With contraction of the lats, the thoracolumbar fascia tightens, increasing spinal stability. If you contract the lats and the glutes at the same time, you’re tensioning the thoracolumbar fascia from the top and bottom.
4. One more muscle that needs to be functioning properly
Muscle we’re talking about:
Don’t forget about the 6 pack maker...rectus abdominis. This muscle always seems to get thrown by the way-side because of how important the transverse abdominis is. It provides forces that allow for vertical stabilization between the rib cage and the pelvis. Don’t focus on crunches to make the rectus abdominis stronger/more coordinated; instead, focus on co-contraction exercises with the glutes and latissimus muscles.
If we just trained the glutes and lats, doesn’t that seem like an awful lot of extension muscle system training (posterior chain) without any recognition of the front side of the body? Training the rectus abdominis to stabilize while performing open kinetic chain and closed kinetic chain movements with dumbbells, resistance tubing, and cables seems like the best bet to use this muscle the way it was intended. As a patient progresses, moving from single plane exercises, to multiplanar, multidirectional, and PNF patterns starts to promote proper stability and coordinated musculature in functional daily positions. 
5. Things I left out
Yep! There’s even more that can aid proper lumbopelvic function and core strength. I tackle these muscles and their roles on a case-by-case basis.
1. The piriformis can tension the SIJ capsule and increase the compression of the SIJ through its attachment to the sacrotuberous ligament.
3. The adductor muscles never seem to get any love either and I didn’t help with that. They are considered primary postural muscles as well to control the hip in standing and midrange walking, but because they are so large, they can also function as prime movers of the hip.
In closing, don’t skip the small stuff when treating lumbopelvic pain and dysfunction. Even those really well-built athletes coming in with back pain can have dysfunction and atrophy of the deep core muscles. However, never stop at the deep core, always progress to larger, and primary muscles stabilizing the spine to make sure they are all functioning appropriately, and never forget the important glute complex, lats, and rectus abdominis when retraining patients in functional exercises for lumbopelvic stability.
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