Functional Anatomy of the Core
The rectus abdominis displays a mainly sagittal nature. The internal and external obliques have a frontal and transverse propensity. The transversus abdominis has a transverse directionality. It is collectively that this muscular design gives us strength, much like the layers of a ply board. This also gives humans an ability to move in all three planes reflective of the fact that we DO actually move in all three planes.
Image 1. Anatomy of the Core
The need for movement of the upper and lower extremities during training to gain core reaction is explained by looking at the origins and insertions of the trunk muscles. The rectus abdominis runs from the pubis at the base of the pelvis up to xiphoid process on the sternum and 5th to 7th ribs. This interconnection of the pelvis and ribcage means movements at the hip or shoulder will affect the actions of the rectus abdominis. Therefore when training the core which includes the rectus abdominis, it is obvious the arms and legs should be employed to gain the maximal muscular response.
As an example, a simple forward step will force the rectus sheath into extension in relation to the anterior pelvic tilt created. This means it eccentrically lengthens creating tension and decelerating flexion of the upper body. The external oblique (EO) shows equal link between the ribcage and pelvis. It originates on the 5th-12th ribs and inserts on to the iliac crest. As we step we create lateral flexion to the side of the ipsilateral leg shortening the EO in the frontal plane and rotating towards the ipsilateral leg lengthening it in the transverse plane. The internal oblique (IO) meanwhile runs from pelvis (iliac crest, ASIS) on to the 10th-12th ribs. It will shorten on the ipsilateral side in the frontal plane and transverse planes. The transversus abdominis (TvA) originates on the 7th-12th costal cartilages and inserts onto the pelvis (iliac crest and ASIS). It will unilaterally rotate the trunk to the same side. This means that it will shorten on the ipsilateral leg during stepping in the transverse plane, while lengthening on the contralateral side as the spine rotates towards the ipsilateral leg. Although not well documented, it could be suggested it would also shorten in the frontal plane with ipsilateral lateral flexion. It would therefore lengthen on the contralateral side during a forward step.
If we can produce all these muscular reactions through simply stepping forward, why would we not use a split stance or step during functional core conditioning or as a response to LBP. Imagine the reactions we can also create by incorporating the arms!
Although different planes are utilized during traditional “core exercise” and the multi-directional nature of muscles has been recognized, the sagittal plane still dominates the majority of movements. Simply by staying seated, the ability of the body to gain movement especially in the transverse and frontal planes, is greatly reduced. This is through decreased proprioceptive interaction with the lower extremities, which is vital to effective pain free movement.
Many of the population could be described as dysfunctional in the sagittal plane by displaying a Kyphotic posture. According to Fryette’s three laws of spinal dysfunction, specifically the third law later added to by Nelson, when excessive motion is experienced in one plane e.g. flexion (sagittal), it will modify (reduce) motion in the other two planes e.g. the transverse and frontal planes. By concentrating actions in the sagittal plane, generally flexion, in a concentric or isometric way there is a reduction in the three-dimensional activation of the core. This possibly leads to dysfunction and pain. Gravity and adaptive shortening of the trunk muscles due to a sedentary desk based lifestyle has already reduced the typical clients ability to move. So, is recreating these conditions an effective training methodology? By training your client to be able to concentrically load into extension as well as flexion, he or she will enable more multi-plane activation of the core. This can be accomplished just by using functionally authentic body positions and movement patterns.
Image 2. Overhead Medicine Ball Throw
The overhead medicine ball throw has high muscular demand, creates functional ecconcentric reactions and is very dynamic.
The more dynamic the movement, possibly the more core and lumbar stability is actually created. Mcgill and Cholewicki found that activities that have high muscular demand actually create more stability at the lumbar spine than those with reduced movement. He states; “Therefore, there appears to be an ample stability safety margin in tasks that require lots of muscular effort”. Greive et al. add “tasks that demand very little muscle activity... are characterized by low spine stability”. By making use of dynamic movements, more of the trunk will be engaged by the trunk muscles. Consequently, more spinal or core stabilization is generated. Most core exercise challenge clients to remain stable, thus reducing dynamic muscle activation.
Lumbar Pain and a Functional Rationale
By using gait cycle dysfunctions as biomechanical examples that relate to the vast majority of people, it can be understood that a ‘weak core’ is probably not the root cause of many cases of lumbar pain.
The lumbar spine has only 5 degrees of rotation. This indicates that it is designed to move minimally in the transverse plane and transmit rather than absorb or decelerate transverse plane forces in this area. When the muscles in and around the hip do not effectively eccentrically load into internal rotation, this may create an environment for lumbo-pelvic dysfunction to occur. If effective eversion of the calcaneus is not achieved, the talus and tibia above will not collapse into internal rotation. This forms a component of the triplane load of pronation of the foot. This tibial internal rotation also drags the femur into internal rotation eccentrically loading the hip musculature. If this load does not occur the foot cannot have the correct positive influence on the lumbar spine through internal rotation at the hip driven distally.
If eversion of the calcaneus does not occur and reduces resultant internal rotation, then this also has implications for the ability to gain dorsi flexion and flexion of both the knee and hip. If flexion does not take place then ground reaction forces cannot be attenuated and the force could transfer higher up the chain, possibly jarring the lumbar spine. It could also lead to excessive lumbar flexion resulting in pain and structural degeneration.
Incorrect foot and ankle mechanics can lead to ineffective hip extension. Tight hip flexors that are unable to get through dynamic hip extension, possibly due to a lack of ability to load in all three planes, can cause the spinal processes to crash together the net result being lumbar pain. If facet joints do not have gapping occurring in all three planes during hip and resultant lumbar spinal extension, then great pain or discomfort could be experienced as they compress.
If this relationship is compromised and resultant hip extension poor, a strategy that the hip may employ is to externally rotate to reduce muscular tension when the heel rises. This could be described as a medial heel whip when witnessed at the lower extremity. This motion driven at the hip joint can also cause excessive rotational forces at the lumbar-sacral or SI joints through the attachment of the psoas between the femur and lumbar spine. This can lead to pain at the low back area that does not want to move excessively in the transverse plane. The femur, pelvis, sacrum and lumbar spine all work in close relationship. Anything that disrupts this symbiotic sequence can lead to pain. Motions at the lumbar spine in gait are predominantly generated distally. Extraordinary force that is generated proximally and out of sequence such as lumbar segment or sacral motion will upset this sequence that should see pelvic motion occurring faster and first.
The psoas’s design is possibly to reduce rotational forces at the lumbar spine on top of the structural limitations already present. The deep attachments at L4-5 are likely oriented to keep the pelvis and spine in a close relationship. If a strong muscular attachment was not present then as the pelvis rotated the relative rotation at the L-5 would be much greater as much more dissociation would occur at the joint and greater rotational torque created. This muscular attachment lessens and becomes more superior as it progresses further up the lumbar and thoracic spine. This allows for more segmental motion superiorly while keeping the relative motion and force at each vertebra smaller inferiorly. This means it can transmit rotational force rather than absorb it through eccentric deceleration. When the lumbar spine has to absorb force is usually when dysfunction occurs.
If the muscles of the hip extensor group’s proprecoeptive information flow are compromised, then ineffective tension regulation can occur. This can lead to muscle spasms, usually during motions into flexion. The muscles can rapidly and painfully contract to protect themselves from potentially increased harmful motion that is outside of their available or perceived range of movement. This could be caused by the contralateral legs lack of hip extension. This creates ipsilateral reduced stride length and therefore, reduced force exposure, resultant hip joint flexion and the muscular range of movement decreased. If the hip extensors do not decelerate flexion, then the muscles above the hip at the spine may have to create more deceleration motion than they are able to. This causes the superior bone to flex on the inferior segment instead of extension being created by the faster flexion forward of the inferior vertebrae. This will also adversely affect various posterior musculatures including around the scapulae where signs of kyphosis are displayed.
The response to this lower back pain should be to discover the root cause of the problem. However, the strategy is to attack the site of the pain at the lumbar spine or the perceived problem the core which attaches to it. In these examples the root cause is probably the lack of 3-D motion at the hip and its relationship with the foot, which untreated, will continue to cause problems in the long term regardless of the level or amount of core focused exercise.
These same stresses could also affect the sacroilliac joints, again resulting in lower back pain. Eccentric loading of the external rotators (glute max, med, min, piriformis) creates muscular tension and increased compression forces at the SIJ reducing shearing forces. J.J.M Pell et al found that “From a biomechanical point of view, an active muscle corset that increases compression forces between the coaxial bones and sacrum could protect the ligamentous system” they also add “Interlocking of the SIJ maybe promoted by transversely orientated muscles” G Lehman et al. say that “reflexive muscle activation relationship has also been demonstrated between the discs and multifidus and the SI joint and gluteus maximus, multifidus and longgissimus.” The inadequate propulsive ability of the opposite foot during the swing phase of gait can be responsible for the lack of proximal (pelvic) drive that leads to internal rotation of the standing leg (femur). This lack of internal rotation will not provide the compression forces described by G Lehman. The culprit in this case could again be the foot.
Limitations in frontal plane motion above at the thoracic spine and/or pelvic translation below could also have implications for lumbar disc integrity. A lack of lateral flexion to one side will increase compressive forces on one side of the vertebrae. This can lead to prolapsed or herniated discs and pain. Is the answer to work the core or create more motion at the thoracic spine that has the propensity to become hypo mobile? The site of the problem would appear to be the thoracic spine and therefore the correct course of action would address this problem.
A function related in sync (thoracic and pelvic rotation in the same direction) example of hip dysfunction that can cause lumbar pain is the golf swing. The pelvis and spine are rotating in the same direction. However if the ipsilateral hip to the backswing has reduced internal rotation then the real pelvic rotation to the same side is compromised. This means that because of the major force coming from above at the hands, the rotational motion at the superior spinal segment is increased as the inferior section closest to the pelvis is prevented from following due to the limitation at the hip. Guess what?? This can lead to pain.
Taking these functional examples into account, working the core in a non-functional and non-dynamic way would be an ineffective method of reducing lower back pain. In some of these circumstances, just creating eversion of the calcaneus or hip extension in functional positions that would allow natural muscular loading to happen would be much more powerful and efficient for reducing low back pain and also increasing core activation. These are just a few functional rationales for the cause of LBP and the individual origins of LBP are many and varied. The true power is the ability to understand, assess and treat the dysfunctions present in the individual in a functionally authentic manner.
By understanding more about why LBP may happen. The focus can shift away from the basic and ineffective methodology of working the core through generic, un-functional and proprioceptively barren exercises. Switching the attention from the trunk to other areas may have more impact on decreasing LBP and increasing core activation.
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