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Pressurization As
Applied To Spinal Stability
Abstract:
There is a positive correlation between spinal stiffness and spinal stability. It is the intent of this author to present what is known as the integrated system of the thoracolumbar fascia. Thus, a comprehensive view of internal muscles of the back, deep contractile tissue of the abdominal wall, and musculature of the lower limb must be analyzed. It is essential to note that extrinsic factors, based on motor command, may be the indispensable key to spinal stability. Complex studies representing motor learning and recruitment patterns of successful lifters, as contrasted to those with back pain, will be assessed. Moreover, that assessment will lead to corrective and optimizing patterns for the benefit of each reader. Further intricacies discussed include: proprioception of the lumbar spine, mechanics of the nucleus pulposes, annulus fibrosis, and the multisegmental system, which comprises the vertebral column.
What is stability? Webster's defines it as ”1. the quality, state, or degree of being stable: as a: the strength to stand or endure: FIRMNESS b: the property of a body that causes it when disturbed from a condition of equilibrium or steady motion to develop forces or moments that restore the original condition c: resistance to chemical change or to physical disintegration. Jesus compares and contrasts stability vs. instability as follows: ”Whosoever cometh to me, and heareth my sayings, and doeth them, I will shew you to whom he is like: He is like a man which built an house, and digged deep, and laid the foundation on a rock: and when the flood arose, the stream beat vehemently upon that house, and could not shake it: for it was founded upon a rock. But he that heareth, and doeth not, is like a man that without a foundation built an house upon the earth; against which the stream did beat vehemently, and immediately it fell; and the ruin of that house was great (Luke 6 47-49).” Thus, we can think of stability as a concept which encompasses a system's ability to resist that which interferes with equilibrium, be it static (none moving) or dynamic (you are unmoved from your path of motion). When we analyze the trunk’s resistance to outside forces, our focus should be on its central axis, that is, the spine or vertebral column. Joe King, when speaking on this subject, will emphasize a fact of correlation. He states that, ”the more mobile an object, or joint is, the less stable it becomes, and vice versa (27).” When studying articulations, one must keep such a notion firmly in mind. The joints created by humeral-forearm (elbow) interactions can be thought of as stable hinge joints, in which segmental motion occurs (occurring at a single segment). However, the spine is comprised of numerous adjacent (stacked one on top of the other) vertebrae, capable of an equally numerous amount of movements, much like an accordion. Therefore, a more complex system dependent on both intrinsic (ligament us and muscular) and extrinsic (neurological) support must be in place. Purpose Outlined Why focus on this subject? To be frank, if your spine snaps, you snap. Consider it as the rock that one must build their foundation on. It is almost impossible to work through back pain, and dehabilitating to drudge through a serious spinal injury. We are not dealing with a light paper here, but rather one that is fundamental to your career, and your ability to train and function with 100 percent intensity. It must be clearly understood that spinal stability is directly correlated to how stiff the vertebral column actually is. When measuring this aspect, Cholewicki et al. states that, ”The determination of lumbar spine stability is accomplished by measuring the instantaneous trunk stiffness in response to a sudden load release (4).” This again goes back to the mobility principle discussed above. It also corresponds with the spine's ability to deform and return to its original shape, a concept known as elasticity. We begin by narrowing in on the latter. Spinal Mechanics
The vertebral column is a multi-segmental
system. The vastly moveable aspect (pre-sacral) of the spine is composed of 24
unfused
Our main concern herein will be to review those moveable structures which bear the greatest loads during most compound movements. These are the thoracic and lumbar regions. The former has a built in protective zone, due to its association with the ribs. These act like powerful splints, stiffening and limiting the motion of this region. As Joe stated, this will drastically enhance their stability. It would therefore behoove us to narrow in further to the lower back, which is composed of five vertebrae. Notes: The sacrum are composed of fused, immobile vertebrae. Several important muscles of the gluteal region find their attachments on the sacrum; additionally, it serves as a strong base which takes forces sustained by the column and transfers them to the hip laterally, due to the joint it forms with the Ileum (this is what your belt rests on). The coccygeal region is also of vital importance, as several muscles of great importance find their attachment points here. Lumbar Vertebrae
As you realize from my articles on back
anatomy, each vertebrae is composed of a flat body anteriorly, which articulates
with the body of adjacent vertebrae above and below it (or rather the
intervertebral disk between them). The vertebrae in this region have an
interlocking design, which limits a good portion of motion (11, 22). Compare and
contrast the mobility of the cervical and lumbar regions to see just how
effective this is. However, there is still considerable freedom. Another
mechanism to guard against compressive forces comes in the actual shape found
within the bones. Pressure is defined as ”force per unit area (40).” Note that A is inversely proportional to P. That is, the larger the area, the lower P becomes. Realize that the lower you travel down your spine, the larger the load the bones must bear. To compensate for the increase in F, the body increases A, meaning the bodies of the lumbar region increase in circumference from L-1 to L-5. Two joints are found posteriorly, via the articular processes, as can be viewed below. Elasticity is defined as the ability of a tissue to deform, and return to its original shape. The ”elastic limit” can be thought of as the point in which the tissue can no longer return to its original shape, or rather it reaches a point of “plasticity (40).” Vertebrae are lined on the outside with cortical bone (the denser type of bone), and filled in with cancellous, spongy, or trabecular bone. This type of arrangement, combined with other mechanisms discussed shortly, provides a witty shock-absorption system. For example, in the scientific journal, “Bone,” it was shown that even after a vertebra was crushed, it regained 94 percent of its original form! “Specimens of human vertebral cancellous bone
were compressed to well past mechanical failure (15% strain) in the infero-superior
direction...With removal of the load, all specimens recovered at least 94% of
their original height (9).” The intervertebral disk is a fascinating and wonderfully made contraption. It consists of an outer, less hydrated region known as the annulus fibrosis, and progresses into a central and highly hydrated region known as the nucleus pulposes. Collagen fibers have a tensile strength comparable to steel (39). It is the organization of these fibers, however, that astounds scientists. First, the disk is composed of fibro-cartilage. This type of tissue is A-Vascular, or without blood vessels. The vertebral disks sustain far too great a load to be a bloody tissue. That is, if they relied on blood vessels to supply their nutrient needs, the compressive forces would hinder blood flow and ultimately lead to localized tissue anemia. The collagen fibers of the cartilage are constructed much like plywood in an up to 20 layer fashion (34). Additionally studies show this region to contain several elastic fibers, which actually provide it the ability to store energy when compressed and, due to its architecture, the cartilage acts as a stupendous shock-absorber. Another vital aspect which we will discuss further into the article is the concept of proprioception. The annulus fibrosis contains numerous mechanoreceptors, which greatly enhance this essential sense! Roberts et al., in the journal, “Spine,” states that, “Mechanoreceptors were found in the outer 2-3 lamellae of the human intervertebral disc and anterior longitudinal ligament. Physiologic studies in other tissues indicate that these provide the individual with sensation of posture and movement, and in the case of Golgi tendon organs, of nociception. In addition to providing proprioception, mechanoreceptors are thought to have roles in maintaining muscle tone and reflexes. Their presence in the intervertebral disc and longitudinal ligament can have physiologic and clinical implications (28).” The nucleus pulposus is perhaps even more astounding. It is composed mainly of water, with a mixture of elastic fibers, and a gelatinous forming substance made of proteins and carbohydrates (22). Such a structure provides your disks with what is known as a hydraulic load bearing system. Blaise Pascal (1623-1662), a brilliant philosopher and scientist, discovered what is now rightfully known as the Pascal principle. It can be defined as follows: Pressure applied to a confined fluid is distributed equally in all directions (10). 1. A compressive (crushing) force is applied
to a vertebral disk. Your next question may concern the avascular state of the cartilage. After all, this tissue is composed of living cells known as chondroblasts and chondrocytes. The answer is contained in the nucleus's ability to bind water. This structure has a high osmolarity, meaning it can actually draw fluid into its direction. As it does so, it hydrates the annulus fibrosis. Upon compression, fluid also is distributed to the AF. A remarkable system indeed. The Ligaments Role In The Creation of a Protective Reflex Arc The vertebral column is enforced with numerous ligaments. For example, on the ventral surface (frontal) of the vertebral column lies the anterior longitudal ligament. It enforces the anterior portion of the vertebral bodies and anchors hard on the sacrum (11). It resists forces from separating adjacent vertebrae, and resists overextension of the spine. The posterior longitudal ligament also resists separation of the vertebral bodies, along with several other supporting structures (there are five other ligaments which will be discussed in future articles). Thus, there is a primary role in keeping the vertebral column together. However, their function in supporting the
spine from ”buckling” takes on what Mr. Knowlden emphasizes as an irreducibly
complex system (19). That is, all the factors at work within the spine are
either simultaneously in place or the column will fail. According to Lucas et
al., without support from surrounding muscle groups, the spine would buckle
under as little as five pounds (21)! The problem, however, is that such support
must be highly coordinated, with uncanny precision and flawless instruction from
the nervous system. How is this accomplished? A closer look at the ligaments
of the spine can shed light on the subject.
Solomonow et al. found a critical reason for this enriched supply of neural elements; they call it the “ligamento-muscular stabilizing system of the spine (33).” That is, the mechanoreceptors (receptors sensitive to movement) so thoroughly innervate the ligaments, due to their vital importance in forming a reflex arc, sensitive to specific movements. To clarify further, specified movements call for specified stability. Reflex arcs are designed to accommodate and adjust to these movements immediately! Here is a summary of their paper (33): Emphasis
Experiment To Confirm Emphasis
Conclusions
In summary The Thoracolumbar Fascia and Its Vital Component In Lumbar Stabilization The Thoracolumbar fascia is perhaps the focal point of this article. Anytime you see a term that appears new to you when studying anatomy, simply realize that the name normally indicates much about it. You can deduce from the name that this is a thick sheet of dense connective tissue (fascia), and that it spans the thoracic and lumbar regions of the body. This connective tissue is composed of three layers. The first two are known as the anterior and middle aspects. These layers attach to the transverse processes of the lumbar vertebrae, then the fascia moves out laterally and blends with the fascia of the transversus abdominis and internal obliques. To clarify, let’s examine what transverse processes actually are. When a thin person bends their back, you can see their spine. In anatomical terms, the bumps you see poking out of the back are known as the spinous processes of the vertebrae.
Secondly, I stated that after its attachment
to the transverse processes, the fascia moves out laterally and blends with the
fascia of the transversus abdominus and internal obliques. Why is this
important, you ask? Because through this interaction, the spine is able to
interact, not only with deep muscles of the back, but also with the abdominal
wall. Thus, a 360 degree functional complex is formed, capable of producing
spinal stabilization mechanisms that will blow your mind!
As the picture above indicates, the transversus abdominis and the thoracolumbar form a hoop structure around the lumbar region of the body, which has great significance. The internal oblique also has origin attachments on the thoracolumbar fascia, and the lower 4 ribs, and inserts on the linea alba (11, 22). Both of these muscles function to draw the abdominal wall inward, which leads us to our next subject, namely intra-abdominal pressure via the co-contractile method of recruitment. Intra Abdominal Pressure Defined 1n 1987, one of the world’s most brilliant scientists conducted what can only be considered as both an innovative and ingenious experiment. He inserted balloons in the abdominal cavities of cadavers, and noted a 23 percent increase in trunk stiffness when inflated to 60 mm hg, and a 43 percent increase in trunk stiffness when inflated to 120 mm hg (35). The balloon effectively increased intra abdominal pressure. The experiment also demonstrated that the firmness of the spine is directly proportional to intra abdominal pressure. That is, the higher the pressure, the greater the stiffness. It will help to see a diagrammatical rendition, based on Tesh's experiment.
Note above that the oval object represents the abdominal cavity, and namely the viscera (internal organs) and the spine is the vertical line. When the abdominal cavity is compressed during hip flexion, the pressure in the cavity increases and it exerts a force against the diaphragm upward, the pelvis downward, and the spine posteriorly. In doing so, as you come back up, this pressure assists in extension. Additionally, like a balloon, the intra abdominal pressure resists flexion of the spine (note how it is pushing against the spine in the opposite direction of flexion), and also resists hip flexion. This is not the only way to increase abdominal pressure, however; as you have seen above, contraction of the transveris abdominis and internal oblique also accomplishes this. In the above diagram, the length of the
arrows represent the magnitude of force produced against the surrounding
structures. Note that as the abdominal wall is pulled in, the magnitude
increases. One method of finding if a muscle group is vital to spinal stability
is to analyze how the nervous system recruits it. It is interesting to note
that this sophisticated supercomputer realizes this, and will increase abdominal
activity under high fatigue movements. Essendrop et al., in the “European
Journal of Applied Physiology,” tested what the nervous system would naturally
do when the spinal erectors were extremely fatigued, using various back
extension resistance exercises. It was found that as the spinal erectors
fatigued and could not contract as efficiently or as strongly, the muscles of
the abdominal wall increased in activity, and with them intra abdominal pressure
(8). This provides great evidence for the abdominal wall to enhance stability
of the spine. When IAP was increased artificially to approximately 15% of the maximum IAP amplitude that could be generated voluntarily with the trunk positioned in flexion, a trunk extensor moment (approximately 6 Nm) was recorded. Although the net effect of this extensor torque in functional tasks would be dependent on the muscles used to increase the IAP and their associated flexion torque, the data does provide evidence that IAP contributes, at least in part, to spinal stability. In 2003 Daggfeldt et al. devised a
“biomechanical model of lumbar back extension over a wide range of positions for
the lumbar spine, incorporating the latest information on muscle geometry and
intra-abdominal pressure (IAP).” It was found that “IAP (measured during torque
exertions) contributes about 10% of the total maximal voluntary back-extensor
torque and that it can unload the spine from compression (5).” To test how the
body guards against sudden loads, Essendrop and colleagues tested how elevated
levels could counteract such forces. In summary of their results, “EMG, IAP,
and movement of the trunk were measured. It was found that IAP of a size likely
to appear in work situations, and the concomitant increase in muscle
co-activation, increased the spine stiffness. This increase in stiffness
decreased the movement caused by the sudden load (7)." Further Hardcore Support!
Artificial examples of such support include
the neck brace, the elbow brace, and any body part wrapped with an ace bandage,
such as the wrist or knee. In the first example, the neck brace stiffens the
cervical region, and at the same time protects it from injury. The transversus
abdominus acts to literally draw the abdominal wall inward. Wilson et al., in
the “Journal of Strength and Conditioning,” states that, “This can be
obtained by performing the ‘drawing in’ maneuver...This technique involves
having the athlete ‘suck in their gut’ by pulling their umbilicus posterior and
superior from their beltline. It is important that the athlete continues to
breathe during this exercise...(6).” The umbilicus is the bellybutton. “The study findings provide evidence that the conscious and automatic patterns of abdominal muscle activation can be altered by specific exercise interventions (25)." These same scientists have also teamed up,
with the addition of Dr. Phyty, for an even more precise study. Here is a
summary of what was found (38): Such results are of paramount importance to the bodybuilder, and I submit to you that optimal programming of your motor system will enhance all your lifts in more ways than one! Re-Programming The System In order to sufficiently program the system, each component must be reduced. The thoracolumbar fascia is the center of what can be classified as an "integrated” system. What does this mean? It means that several muscles have attachment points to this connective tissue. The lattissimus dorsi attaches the upper extremity to this region, and the gluteus maximus is also associated with it. To clarify, the lats actually insert onto the humerus, furthering the connection, and the gluteus maximus inserts on the femur, or thigh bone. The system is nothing short of genius. Any movement which requires the lower body incorporates gluteal contraction, which automatically increases spinal stability! Vleeming and colleagues did much to conform this integrated system. They tested how much tension was measured in the TLF with a number of muscles. It was found that, “Traction to a variety of muscles caused displacement of the posterior layer. This implies that in vivo, the superficial lamina will be tensed by contraction of various muscles, such as the latissimus dorsi, gluteus maximus and erector muscle, and the deep lamina by contraction of the biceps femoris.” From these results, the following conclusions were drawn (38): “Anatomic structures normally described as hip, pelvic, and leg muscles interact with so-called arm and spinal muscles via the thoracolumbar fascia. This allows for effective load transfer between spine, pelvis, legs, and arms--an integrated system.” They postulate that, “the combined action of these muscles assists in rotating the trunk, while simultaneously stabilizing the lower lumbar spine and sacroiliac joints.” The author mentioned above by the name of Eric Wilson, also concurs with their results by stating that, “The TLF is connected to the upper extremities by the latissimus dorsi and to the fascia lata by the gluteus maximus muscles. Targeting the latissimus dorsi and gluteus maximus is also important because of their contralateral coactivation capability, thus strengthening the latissimus dorsi assists the gluteus maximus in generating force and vice versa (6).” The significance of this cannot be overstated, especially when programming the nervous system. What I have done is further research the importance of when an athlete should contract the gluteus maximus, in relation to a lift. I found that Dr. Noe and colleagues had performed a magnificent study on the subject (24). They wanted to test hardcore, experienced weightlifters who have sustained incredible loads with minimal back disturbance. I believe Mr. Blood Stained Shins Powell would approve of the study, as it incorporated deadlifts!
Muscles tested included the "gluteus maximus, quadriceps, latissimus dorsi, and erector spinae in 4 weight lifters and 11 asymptomatic control subjects.” That is to say, that the hardcore, experienced lifters’ recruitment patterns were directly compared to non-effective lifters to find what exactly was the difference in their recruitment patterns. It was found that “the weight lifters achieved maximal force at 50% of maximal lift height, whereas the control subjects achieved it at 67%.” This is a tremendous difference. The authors noted a significant correlation between early gluteal contraction and maximal force generation. That is, the experienced lifters contracted this region much quicker than their counterparts. It was also noted that “This process would stabilize the pelvis and permit the erector spinae to extend the trunk more efficiently.” Recall that the TLF is composed of three
parts. The first two attach to the transverse processes of the lumbar region.
The third section, however, attaches to the spinous processes of the thoracic,
lumbar, and sacral region. Thus, when the internal abdominal unit contracts
laterally, or when complete circular tension is used like a neck brace to
stabilize the spine. However, the gluteus maximus is associated with the aspect
of the TLF, which finds its attachments on the spinous. Once again, the Lord
spared no expense here, as this muscle group has a direct line of pull to the
specified region. 1. Stand up, and imagine that your shirt is
the thoracolumbar fascia. Achieving Peak Spinal Stability 1. Studies show that endurance of the trunk
musculature is an extremely vital component. You must be able to both recruit
and maintain strong recruition throughout a set. For example, during a set of
squats, if you lose your ability to co-contract the muscles which draw in the
abdominal wall, your spine will no longer have sufficient support and injury is
likely to occur. Such a concept is especially vital to the bodybuilder, who is
no stranger to long and hardcore sets. Exercises To Incorporate 1. Abs At Work - While at your desk at work,
you will want to practice drawing in the abdominal wall while seated in a
correct posture. That is, with a normal spinal curvature. Simply draw in the
belly button toward your spine and hold it in tight. The goal is to hold it as
long as possible while still breathing. I suggest a progressive application
like so: Perform 4 more identical to it. 3. Straight Arm Pulldowns WIth Stabilization
- Straight arm pulldowns are a "straightforward” exercise. Simply attach a
short bar to the high pulley extension, and place your hands on the bar (palms
down). Normally you would simply pull the bar straight down towards your legs,
with your elbows extended the whole time. Such an exercise targets the lats,
for example, and other extensors of the humerus. However, this is not simply a
lat exercise, but a re-programming sequence. The weight should be relatively
light to begin. No more than 50 percent of your max. Again, begin with your
hand on the attachment. Before lowering the weight, draw in your belly button,
followed immediately by a contraction of the gluteus maximus. Now pull the
weight down. Following this, you will go back to the beginning aspect of the
exercise (i.e. let the weight come back up while resisting it), and as you reach
the starting position, release the contraction of the gluteus maximus, and then
release the drawing in of your abdominal wall. You will repeat for 30-60
repetitions. This develops motor learning, as well as endurance in the target
musculature. We often refer to those without strength as
“spineless” or “without a backbone.” It was my sincere hope to show you the
truth of these sayings today. Do not expect to succeed with as glaring a weak
point as a weak back. Conversely, expect to clarify the path toward your
athletic endeavors by strengthening this region and all aspects which are
intimately associated with it. References: 1. Bogduk N, Twomey LT: Clinical Anatomy of The Lumbar Spine. New York: Churchjill-Livingstone 2. Callaghan JP, Patla AE, McGill SM. Low back three-dimensional joint forces, kinematics, and kinetics during walking. Clin Biomech (Bristol, Avon). 1999 Mar;14(3):203-16. 3. Cholewicki J, Juluru K, McGill SM Intra-abdominal pressure mechanism for stabilizing the lumbar spine. J Biomech. 1999 Jan;32(1):13-7. 4. De Troyer A, Estenne M, Ninane V, Van Gansbeke D, Gorini M Transversus abdominis muscle function in humans. J Appl Physiol. 1990 Mar;68(3):1010-6. 5. Daggfeldt K, Thorstensson A. The mechanics of back-extensor torque production about the lumbar spine. J Biomech. 2003 Jun;36(6):815-25. 6. Eric Wilson REHAB TIPS: Neuromuscular Reeducation and Strengthening of the Lumbar Stabilizers. Strength and Conditioning Journal: Vol. 24, No. 2, pp. 72–74. 7. Essendrop M, Andersen TB, Schibye B. 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