Traditional anatomy descriptions of the
spinal muscles have only taken a look at
the posterior view or from the back.
Muscles are typically studied or viewed
as straight line cables.
A more current understanding of muscle
anatomy involves how movement is created
and joints are stabilized.
Many anatomy books describe the function of
the rotatores as small rotator muscles of the
spine. The intertransversarii as lateral flexors of
According to McGill (2002), these muscles
are very tiny and do not create movement.
• However, they may function as vertebral
position sensors at every thoracic and lumbar
Extensors of the Vertebral Column
The major extensors of the thoracic and lumbar spine.
The role of these muscles is different in the two areas
of the spine.
These muscles attach to the ribs and the thoracic vertebrae
with long tendons that run parallel to the spine and attach
at the sacrum and iliac crests.
The thoracic extensors run just under the fascia over the
These extensors have the greatest moment or torque.
According to a study from the American
Journal of Neuroradiology 2005, the
development of extreme thoracic kyphosis
might contribute to excess biomechanical
stress in the spine and may identify a
population at risk for future vertebral
compression fracture at the thoracolumbar
These muscles originate over
the posterior sacrum and go
at an angle and deeply
attach to the lumbar
Injury or load to the lumbar
spine increase when there is
flexion of the spine. These
muscles lose their angled
attachment with spinal
flexion increasing the load or
force to the spine.
The extensors of the lumbar
spine create a shearing force
This is, unfortunately, the
way most people bend over
to pick something up.
Therefore, increasing risk of
injury to the spine and
During lifting, muscles and ligaments significantly
increase loads to the spine.
In weak spines, a spinal load of 7,000N or 1,560lbs
begin to damage the spine. Think of how many
times you bend over during the day to pick
In young healthy spines, 12-15n or approximately
2,600-3,360 lbs begin to load the spine.
In weight lifters with ideal mechanics, the load can
increase to 4,480lbs.
One avoids injury to the back when you
flex at the hips, therefore reducing or
minimizing tissue tension.
If you are flexed at the hips and not the
spine, there is a increase in thoracic
extensors and the lumbar extensors do
not increase the load to the spine.
The abdominal muscles are activated by
creating a “corseting” effect stabilizing
the spine through abdominal bracing.
According to Callaghan, Gunning and McGill
(1998), to have safe therapeutic muscle
activation for the lumbar extensors, one must
activate one side of the spine at a time.
As discussed previously, there are four sections
of the extensors. Right and left thoracic and
right and left lumbar.
Increases the load to
the spine to 6,000N or
over 1,300 lbs.
It certainly does
activate all 4 sections
but with injury to the
These muscles only span a few joints or
vertebrae and the force they apply is
The multifidus does play a role in
stabilizing but cannot be isolated.
The “lats” are involved in lumbar extension
and spinal stabilization.
The latissimus is active during pulling and
Activated in Bird Dog with arm and opposite
leg activated, rows and pull downs.
Why is it segmented instead of one long
• Possibly to facilitate flexion/extension of the
torso and to assist with abdominal distension
or contraction as volume changes ( M.
Functional point of
• Work together and
• The oblique's create
a twisting and lateral
bend and enhance
• Rectus primarily
Upper and lower
• According to Leman
and McGill, 2001,
there is no separation
of upper and lower ab
The oblique's and the transverse abdominus
form a hoop around the entire torso
creating stability or stiffness for improved
Attaches to T12 and to all
the lumbar vertebrae and
to the femur.
The psoas is a hip flexor
and not a spine stabilizer
Juker, McGill and Kopf,
(1998). This is because it
attaches to the lumbar
vertebrae, creating a
stiffening of the spine
only when the hip is flexed
Attaches to each of
the lumbar vertebrae,
pelvis and rib cage.
The quadratus lumborum, or QL, is a common source of lower
The QL is capable of extending the lower back when contracting
bilaterally, the two QLs of the low back pick up the slack, as it
were, when the lower fibers of the erector spinae are weak or
inhibited (as they often are in the case of habitual seated
computer use and/or the use of a lower back support in a chair).
There is a mechanical disadvantage created by constant
contraction while seated which can overuse the QLs, resulting in
A constantly contracted QL, like any other muscle will experience
decreased blood flow, and will create muscle spasms over time.
True spine stability is accomplished by a balanced
“stiffening” from the entire musculature of the torso.
This includes the abdominal wall, quadratus
lumborum, latissimus dorsi and the back extensors of
longissimus, iliocostalis and the multifidus.
There is not a single muscle that is responsible for
spinal stability like the transversus or multifidus. Very
few individuals can singularly activate these muscles.
By attempting to recruit these muscles by drawing in
ones ab wall, one creates instability when they are
attempting to increase spinal stability by “hollowing”
The core muscles differ from the arm and leg muscles in
that the muscles co-contract stiffening or corseting the
trunk so that all the muscles work together synergistically.
Therefore, training the muscles of the core is different than
training the muscles of the limbs.
The core generally functions to prevent motion rather than
initiate it. Activities of daily living need power to come
from the hips and transmit to a stable torso. Pushing,
pulling, lifting, carrying and efforts of the torso are
compromised by the spine bending or what are called
“energy leaks”. These energy leaks over time can
accumulate and create an injury to the spine.
What are Energy Leaks?
Energy leaks are caused when weaker joints
are forced into eccentric contraction by
Energy leaks are points at which energy is lost
during the transfer of force from the ground.
Energy leaks are a result of the inability of the
body to stabilize a particular joint.
Sitting with a rounded
Squats with rounded
back or knees that cave
Lifting a child, lifting
groceries with a rounded
back poor posture.
Walking or running with
with hips that have a
great deal of
Energy Leaks create
Standing on an unstable surface.
Stretches that emphasize knee to chest
or toe touches.
Using a physioball does not create
spinal stability. To use seated with
rounded posture is a significant “energy
Examples of what can lead to an injury
further up or down the kinetic link.
Over Pronation, Under Pronation, High Arches
Shortened hip flexors
Quadriceps: Rectus Femoris
Lateral hip pain, knee and foot injuries
IT Band Syndrome
Bartynski, W.S, Heller,M.T., Grahovac,S.Z., Rothus, W.E., and Kurs-Lasky, M. (2005) Severe Thoracic
Kyphosis in the Older Patient in the absence of Vertebral Fracture : Association of Extreme
Curve with Age. American Journal of Neuroradiology, 26:2007-2085.
Nitz, A.J., and Peck, D. (1986) Comparison of muscle spindle concentrations in large and small
human epaxial muscles acting in parallel combinations. American Surgeon, 52:273-277.
Bogduk, N (1983) The innervation of the lumbar spine. Spine, 8:286.
McGill, S.M., and Norman, R.W. (1987) Effects of an anatomically detailed erector spinae model on
L4/L5 disc compression shear. Journal of Biomechanics, 20 (6):591.
McGill, S.M., Hughson, R.I., and Parks, K. (2000) Changes in lumbar lordosis modify the role of the
extensor muscles. Clinical Biomechanics, 15 (1):777-780.
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