Elaboration on previous post:
Some of this may come across as technical, but I will try to give real world gym examples so that the compensation movements can be better understood. It is these compensatory movements that end up causing or exacerbating the low back tightness/discomfort.
The lumbar spine works via coupling of functional spinal units. A functional spinal unit being defined as the smallest mechanical unit of the spine and including all structures joining two adjacent vertebrae (ligaments, discs, facets etc). Coupling in the lumbar spine is the combination of the action of the various tissues (muscles etc) to stabilize at each segment.
The lumbar spine is formed of many of these couplings (eg. L1 with L2, L2 with L3…), each working with the other to enhance stiffness and stability. These couplings summate with each other so to speak (to maintain optimal lordosis curve and to resist shear force stresses).
Why is that important? Well, with gross movement patterns such as squats and deadlifts, the larger muscle groups may compensate for deficiencies in the more proprioceptive tissues (eg. lumbar multifidi, rotatores or the like). Essentially, the global mobilizers such as the spinal erectors, which have a primary function of back extension, will take over the stability role from the weak or improperly firing deeper musculature.
So instead of the multifidi being utilized for segmental stability, the more powerful erectors will be called upon to play double duty-gross movement AND segmental stability. The problem with that is those larger muscles don’t have the fine control compared to the smaller, deeper units. They end up tiring out much faster. This is then manifested as that deep, tired or achy feeling, especially with higher repetitions.
Since there is further stability afforded by the “corsetting” action of the abdominal units via the thoracolumbar fascia (as well as increases in intraabdominal pressure), it is important to work on this function as well. The inner and outer core units act much like a brace and help “stiffen” the combination of all those spinal units.
By using neutral spine core exercises such as planks, bridges, birddogs, the compensatory spinal musculature is taken out of the equation to a greater extent. This allows the deeper, proprioceptive tissue to be recruited. These exercises should not necessarily be considered as pure strengthening movements but rather biomechanical retraining movements. When doing them, you are RETRAINING your body to use the deeper musculature for the OPTIMAL purpose: segmental control and stability.
So going back to the tight psoas example: the tight hip flexors will cause anterior pelvic tilt (which in turn causes lengthening/weakening of the abdominals). If the spine acts as discussed above (as a stiff unit), the expected posture would be one with a forward lean. Typically, one doesn’t see that position.
Instead, we tend to see the compensated position, with the lumbar spine extended and excessive lordosis(extensor torques as described earlier). This keeps the body in a more upright position.
Now take that position and put it in to a squat. There is now a load on the spine. The load will typically tend to cause anterior shear (forward bending). The extensors will resist with greater extensor torques. And there should be balance. Gravity helps on the way down and for most, the descent isn’t too bad.
Now here is where the problems become more apparent. In the bottom position of the squat, there is the anteriorly rotated pelvis due to tight hip flexors (weak abs and glutes; tight spinal erectors-Janda’s pelvic crossed syndrome). This causes the weight to shift further forward.
Once again, the compensation is to fire the spinal erectors to balance the anterior shear forces. This is where the lack of segmental control will now start to show. As the individual stands up, movement is initiated at the lumbar spine (due to lack of segmental control) instead of being initiated at the hips (using larger, more powerful muscles such as glutes/hams).
Essentially, the spine is lacking stiffness and the hips are lacking mobility. This is that hitching referred to in the previous post.
The easiest way to address these issues are to increase hip mobility,increase glute activation, increase spinal stiffness with the correct choice of core exercises, and retrain the squat or deadlift pattern. The last one is the toughest. It requires dropping the weight and making a concerted effort to utilize hip movement over lumbar movement to create the extensor moments.
And that is my ramble for tonight. Hope it makes sense.
That was a great explanation!