news.gif (12017 bytes)  HUMAN POSTURE By Dr. Scott D Neff DC DABCO CFE DABFE FABFE FFABS FFAAJTS Doctor of Medicine

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Liberty You will find in this section hot NEW articles which we feel are of national importance to all folks.  These in-depth scientific forensic works are brought to you as a free service from AAJTS.  If you wish to become a member of the Academy and receive weekly Articles, join now!



     When the eyes and the plane of bite are in the horizontal plane, the head is thought to be in equilibrium.  Equilibrium is maintained through the human lever system of biomechanics.  The fulcrum of action potential is thought by many experts to be acted upon by (Center f Gravity) which is the composite of posterior muscle vectors acting upon the head and neck.  The fulcrum lies at the level of the occipital condyles.  If a force is applied by the weight of the head through its center of gravity near the sella turseca, a force will act thought the posterior neck muscles for counter balance to support the head upon the neck. 

     The center of Gravity force lies anterior to the midline of the Skull.  To counter balance this force, the posterior musculature has greater strength and tonus as compared to the cervical flexor muscles.  Thus, the extensor muscles counter acts the forces of gravity whereas the flexors attempt to assist gravitational force.


2.  Plantigrade Posture and the Human Spine 

     When both lower extremities in the plantigrade posture support the human body symmetrically, the lumbar spine demonstrates an anteriorly convex curve known as the lumbar Lordosis.  Viewed posteriorly, the lumbar spine would appear straight.  When the body is supported asymmetrically, the human spinal curves vary.  Viewed posteriorly, when the body is supported on the left leg primarily, the spinal column demonstrates a curve concave towards the ipsilateral supporting leg.  This results in tilting the pelvis with the ipsilateral support hip rising higher than the contralateral resting hip.  Commensurate with these actions the thoracic column flexes toward the resting limb and the cervical curve is relatively concave towards the supporting leg. 

     In the plantigrade posture, there is a slightly forward bias, counterbalance by tonic contraction of the Gastrocnemius, Soleus, hamstrings and the erector spinae group. 

     As the body is flexed, the paravertebral musculature contracts followed by the glutei, hamstrings and Soleus muscles.  When flexion ends the spinal column is stabilized by passive action of the vertebral ligaments fixed to the bony pelvis, which tilts forward due to the hamstring tension. 

     During extension back to the neutral plantigrade posture the order of muscular recruitment is reversed, with the hamstring first followed by the glutei and last the lumbar ad thoracic musculature.



     Sitting posture is generally divided into three classifications according to Kapandji.  These are Ischial support, Ischio-femoral support and Ischio-sacral support. 

     Ischial support occurs as the person sits up straight without resting on the back of the chair, as in typing.  In this case, the Ischial bones and the pelvis support the weight of the trunk.  This state is unstable loading due to a tendency to tilt forward accentuating the three spinal curves.  This may cause the trapezius and scapular musculature to act as stabilizers.  Thus, this posture may lead to trapezius strain or trapezius syndrome also known as “Secretarial Syndrome”. 

     Ischio-femoral support occurs as the person sits with their trunk flexed.  In this posture the Ischial tuberosities and the posterior aspects of the thighs support the trunk with additional support coming from the upper extremity resting on the knees.  The pelvis is tilted anteriorward and the accentuation of the thoracic curve increases the tendency of the lumbar curve to flatten.  This posture relaxes the posterior musculature and decreases the shearing forces on the lumbosacral discs. 

     Ischio-sacral support occurs as the patient slouches or reclines in a sitting posture.  In this posture, the trunk is supported by the Ischial tuberosities, the posterior surface of the sacrum and the coccyx.  The pelvis is tilted posteriorly, the lumbar curve is flattened, the thoracic curvature increases and the head sometimes lies forward on the thorax, which may lead to inversion of the cervical curvature. 

     Many individuals recline in the orthopedic position with the help of orthopedic beds, reclining chairs and cushions.  In this position, the thoracic curve is accentuated and the lumbar and cervical spines are flattened.  Because the lower legs and knees are supported, the hips are flexed, relaxing the Psoas and hamstrings.



     Generally, the lowest intradiscal pressure and the least electromyographic activity of paraspinal muscles are considered the optimum in reclining pleasure.  The lowest electromyographic and intradiscal pressure recordings were found with a back rest inclination of 120 degree and a 5 cm lumbar support.  The highest intradiscal pressure occurred when there was no spinal support and a 90 degrees inclination (straight back). 

     To decrease the risk of mechanical sciatica developed through the driving of motor vehicles, the use of arm rests as well as lumbar supports is indicated.  Arm rests and lumbar supports decrease intradiscal pressure.  Combining proper inclination of the back rest, proper elevation of the arm rests, as well as lumbar supports and perhaps a leg rest will decrease intrathoracic, intra-abdominal and intradiscal pressures insuring proper rest and relief.



     In the supine position with the lower extremities extended the Psoas is stretched and the lumbar spinal curve is thought to be accentuated. 

     When the lower extremities are flexed at the knees, the Psoas is not under full tension.  This is thought to cause a tilt of the pelvis and a flattening of the lumbar spinal curve.  This position yields little tension of the spinal and abdominal muscles. 

     In the recumbent position, the spinal column forms an almost flattened sweeping S shaped spinal curve.  The lumbar curve becomes slightly convex inferiorly and the mid to upper thoracic spine becomes relatively convex superiorly.  This position does not relax all of the musculature as previously thought. 

     In the prone position, the lumbar curve is exaggerated.  It is thought that this position causes respiratory difficulties from the pressure of the supporting surface on the thorax and abdomen, pushing the viscera back on the diaphragm thus reducing its proper excursion.



     Leg lifting, as opposed to back lifting has received much attention.  However, ergonomics also dictates that the distance of the object from the body at the time of lifting also is important in the proper way to lift an object a given distance.  Simultaneous electromyogram, and intradiscal and trunkal pressure measurements indicate that the greater the distance of the lifted weight away from the body the higher the forces needed.  This is due to increase lever arm work via increase dead.  Intradiscal pressure is increased due to a larger joint reaction due to increased shearing force pressures.  Electromyographic activity is increased due to the greater force exerted by the erector spinae muscles.  Finally, trunkal pressure is increased due to a greater need for trunkal support to protect the spine from incidental postural and motion stress, strains and other motion injuries.



     The study of Ergonomics indicates that pushing an object in a horizontal plane decreases the load on the lumbar spine and discs as opposed to pulling an object in the horizontal plane.  When one pulls an object, this increases the bending moment and the discal pressure.  The erector spinae force must increase considerably to counter balance the bending moment due to these muscles groups short lever arm with respect to the axis of rotation.  When one pushes an object there is a lower load applied to the discs and lumbar curve.  This is thought to be due to the large lever arm the Rectus abdominus muscle group has as opposed to the erecter spinae muscle.



     Coughing, straining, sneezing and excessive laughing may aggravate spinal pain.  Many exercises may aggravate spinal pain.  Forward flexion combined with lifting is associated with increased spinal discomfort.  Sit-ups with or without the hips flexed cause intradiscal pressure comparable to pressure generated by forward flexion of 20 degrees holding 20 Kg.  Thus, sit ups with or without the hips flexed causes large loads to be exerted on the lumbar spine.  However, it should be noted that sit-ups with the knees bent is lower than straight knees. 

     Physicians whose patients have spinal pain should also be directed to avoid straight leg raising exercises and lumbar hyperextension exercises. 

     Obesity greatly increases intradiscal pressure or direct vertical compressive loads on the spine and significantly increases the anteriorly active loads, thus increase joint reaction forces.  Trunkal pressure is increased due to a greater need for trunkal support to act as protection for the spine. 

     Finally warm ups consisting of a hot shower and then slight active motion movements are commenced.  Next stretching would follow to ready muscle and tendon groups as well as ligamentous structures.  Finally, your active exercises or weight lifting would be commence


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