Activating the core and the posterior chain
Here we will briefly discuss strategies for reducing the stress on your spinal ligaments, joints and discs through the use of core stabilizing musculature to help pressurize and stabilize the trunk and the use of the posterior chain to generate power and a foundational stability for the trunk. We have already discussed the neutral spine and the role of the trunk extensors in also absorbing force and the concept of the neutral spine should be active in all of these activities.
Core Activation: Briefly our super simplified anatomy of the core form a cylinder which surrounds our trunk, which of course contains our spine with the structures we are trying to protect, the ligaments, the discs and the facet joints. The goal of core activation is to slightly stiffen and pressurize this cylinder and to maintain this stiffness throughout all of our daily activities, from forward flexion with heavy lifting to walking through the mall to sitting all day at your job, etc etc. Core activation is much simpler than we think, it’s transition from a voluntary contraction in the doctors office to a non voluntary habit the other 99% of your life is what at times can be a difficult transition. Core activation must be constantly practiced, this sets up a motor neuron pattern and helps to facilitate transitioning this into a pattern.
Feed Forward Mechanism: Our core musculature and the supporting system of muscles which function with the core have a certain resting tension to them, that is at rest they are still slightly contracted. There is some stiffness of the ligaments as well, but if we are properly keeping our neutral spine and activating our muscular support system the ligaments should only have stress at the end of our range of motion, which should be avoided in any case.
The muscular support the spine receives can be noted as global stabilizers and segmental stabilizers, although this is much simplified to make it easier to understand, the actual biomechanics are more of a difficult concept. Global stabilizers are the larger muscle groups with a fulcrum farther away from the spine such as the larger trunk extensors the Iliocostalis and the Longissimus. Segmental stabilizers are the smaller more intricate muscles such as the Multifidi which only run from 2-3 spinal segments. These smaller segmental stabilizers have been found to have a richer content of proprioceptive receptors (and to a larger proprioceptive extent the smaller Intertransversii and the Interspinales), which you will recall we discussed proprioception as being our ability to tell where we were in time and space. Thus we have a system of these global stabilizers which function to actually move and stabilize our entire trunk, and we have the support at the segmental or vertebral level of these little segmental muscles which function to move and stabilize smaller units such as the spinal joints and also provide more proprioceptive feedback to the brain which uses that feedback to constantly adjust velocity and force.
Research has shown us that when we initiate a movement a split millisecond before we actually move our brain tells us to further slightly stiffen the trunk muscles to provide trunk stiffness and stability in anticipation of the movement we will be performing, whether it is bending forward to pick up a box, initiating walking, or sitting down. Research has shown us that this feed forward mechanism is impaired in chronic low back pain sufferers, so this person may go about applying a load to his spine through trunk movement but his feed forward mechanism kicks in later than it should and that person performs the motion without the protection of the trunk musculature. This has been found to a greater degree in the smaller segmental stabilizers which is why a rehabilitation program focusing on the larger trunk muscles usually has limited success and many times exacerbates this imbalance by concentrating on the wrong aspect.
More importantly is some of these deep segmental stabilizer muscles actively help to control the movement of the facet joints themselves. Without the help of this stabilizing and modulating system the joints, which are ligamentous structures, are prone to injury, not to mention the stress on the more global spinal ligaments such as the interspinal and supraspinal ligaments.
The intraspinal ligament protects against the shearing force of one vertebra against another when flexing forward, the supraspinal ligament protects against global flexion, and the capsular ligament protects the facet joint itself.
Core Activation/Bracing: Core activation is really a simplistic way of activating these global and segmental stabilizers and relearning the motor patterns of them stabilizing the trunk during movement, sparing the ligaments, joints and discs from stress and damage.
To start stand naturally, remember to have a neutral spine even when simply standing. Simply lightly contract your abdominal region. I say simply, but it is always surprising the number of patients who do not have this proper motor control. I do two things with my patients to help them understand motor control of the core. 1) I have them place their hands on their back with their fingers just to the immediate left and right of the spine so they can feel their extensor musculature. 2) I have them brace their abdomen region as if they are going to be punched in the abdomen. If you properly brace you will feel the low back muscles bulge beneath your fingers, this is the proper activation of the core, specifically the transverse abdominus, the internal oblique and the multifidi, but there is also some global activation here of the larger support muscle groups.
How much brace? Research has found that very little bracing is needed to obtain trunk stabilization. 5-10% muscular contraction is usually enough. Short of carrying around a portable EMG unit (which I’m guilty of) the best way to know you are contracting just the right amount is to take a deep breath in and out. If you can maintain the contraction while breathing deeply in and out this is a good place to start at. Many patients have trouble co-contracting both the diaphragm to breath and the core, I’ve seen this in many chronic low back sufferers. Remember this co-contraction is important as the diaphragm is the top of our core cylinder and provides pressurization to the trunk when properly utilized. Later on in the more intermediate and advanced rehabilitation there are more strategies to teach the patient how to co-contract during for example heavy breathing after strenuous exercise, quite important to the athlete.
So to begin we want to have a neutral spine at all times, especially when doing any trunk movements or activities. We also want to have activate our core by bracing the abdomen properly and maintaining this brace during our daily activities.
Posterior Chain and Pelvic Floor
Pelvic Floor: The pelvic floor musculature is important as the “bottom” to our core cylinder. The pelvic floor helps to maintain proper intra-abdominal pressure. Pelvic floor dysfunction is commonly seen in post partum mothers who can have decreased pelvic floor function after natural child birth. Activation of the pelvic floor can be as simple as performing Kegel exercises or a drawing in of the pelvic floor muscles. These can also be taught as a co-contraction with abdominal bracing. Other times pelvic floor deficiencies can be more complicated and require specialized care.
Posterior Chain Activation: It’s very common to find the inability to activate the posterior chain in the case of the chronic low back pain patient. Our posterior chain provides our foundation for our trunk and helps to provide power such as in walking, running, sitting down and getting up, etc. The posterior chain can also be a powerful stabilizer coupled with the neutral spine and core activation.
At the base of our posterior chain is the Gluteus Maximus. This muscle is primarily involve with hip extension, although with the feet (or foot if we are walking) planted it helps to stabilize the pelvis. When we advocate the increased use of the trunk extensors with a neutral spine posture we are really missing a large part of the equation, that the Gluteus Maximus along with the posterior chain can help to alleviate some of the stress to the trunk and spine including taking some of the stress off the trunk extensors and more evenly distributing that force overall to the body. When teaching patients how to bend to pick up a box off the floor, for example, they are able to hold a neutral spine posture until about halfway down, at this point they are unable to coordinate or activate their posterior chain and put undue pressure on the lumbar extensors, sometimes failing to even do that they lose their neutral posture and devolve into full lumbar flexion, utilizing their hamstrings to help lower themselves at times. Part of activating the posterior chain is learning how to flex the trunk at the hip instead of at the low back.
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Squat: The squat exercise has long been a mainstay of the strength community. From sports teams to bodybuilders the squat has been recognized as one of the best exercises to build lower body strength and more importantly build a neuromuscular coordination with the posterior chain and the generation of power and locomotion. For the moment our discussion lies with unweighted or moderately weighted exercises, concentrating on the motor/movement patterns and the re-establishment of the posterior chain. Being aware of the numerous arguments against the weighted squat in terms of knee injuries and compression to the low back disc we can leave that discussion for another time.
As a side note, we have discussed the commonly seen issue of tight and shortened hip flexors in patients who sit or trunk flex all day. This is an issue which should be concomitantly addressed as proper hip hinging and posterior chain activation depends on proper hip extension, which may be hindered by a dysfunctional antagonistic muscle group. On the same topic tight shortened hamstrings may also apply a propensity to force the low back and hamstrings to become a dysfunctionally large part of the motor pattern instead of the trunk extensors and the posterior chain.
Activation: Due to low back pain and dysfunction the squat, while being a very powerful rehabilitation tool, is not often used as the posterior chain activation. There are a lot of core and muscular relationships which need to be established in terms of a dysfunctional trunk and lower back and it is easier to establish them separately then meld them into the compound exercises. At first it is best to concentrate on the Gluteus Maximus with pelvic tilts and the Gluteus Medius with external rotation. Full dual legged squats may note even be prescribed as we have found success with early Gluteal activation and decreased stress for example with the one legged squat.
Pelvic Tilt: Lie on the floor with your knees bent and your feet flat on the floor. Make sure you initiate a neutral spine while you are lying down and maintain the neutral spine for the duration of the entire pelvic tilt. Place your hands face down near your pelvis, while learning this activation you can place your thumbs on the upper outer portion of your buttocks to give yourself feedback that these muscles are being activated. While “squeezing” the buttock muscles gently raise your pelvis towards the ceiling, I like to tell patients to imagine as if they are lifting a coin from the ground with their buttocks and they need to keep that coin from falling out, an interesting visualization but one that usually helps in activating the correct regions.
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