The muscles responsible for the movements of the spine, with
the exception of two groups, have at least one attachment on the
spinal column or the skull. The exceptions are the abdominal and the
hyoid muscles. Both groups are superficially located on the front
of the body. Nevertheless, both groups, the abdominal muscles in
particular, are effective movers or stabilizers of the spine. The
muscles are listed according to aspect and region.
- Cervical Region
- Prevertebral muscles (longus
capitis and colli, rectus capitis anterior, and lateralis)
- Hyoid muscles (suprahyoids and infrahyoids)
- Thoracic and Lumbar Regions
- Abdominal muscles
- Obliquus externus abdominis
- Obliquus internus abdominis
- Rectus abdominis
- Transversus abdominis
- Cervical Region Only
- Splenius capitis
- Suboccipitals (rectus capitis posterior major and minor, obliquus
capitis superior and inferior)
- Cervical, Thoracic, and Lumbar Regions
spinae (iliocostalis, longissimus, and spinalis)
- Deep posterior spinal muscles (multifidi, rotatores, interspinales,
intertransversarii, and levatores costarum)
- Semispinalis thoracis, cervicis, and capitis
- Cervical Region
- Scalenus anterior, posterior,
and medius (commonly called the three scalenes)
- Levator scapulae
- Lumbar Region
- Quadratus lumborum
- Psoas major
and Functions of Individual Spinal Muscles
As Figure 9.13 shows, the longus colli and capitis extend vertically
up the front of the vertebrae, the colli from the upper three thoracic
to the first cervical (atlas) and the capitis from the lower cervical
to the occipital bone. The rectus capitis muscles pass obliquely
upward from the atlas to the skull, the anterior slanting medially
and the lateralis laterally. With the exception of the longus colli,
these muscles flex the head and neck when the left and right muscles
act together. Acting separately, they flex the head and neck laterally
or rotate it to the opposite side. The longus colli acts only on
the neck and is active in resisted forward flexion, resisted lateral
flexion, and rotation to the same side. It also stabilizes the neck
during coughing, talking, and swallowing.
Prevertebral muscles of cervical spine (anterior view).
Also called the strap muscles, these are small anterior muscles
in the cervical region (Figure 9.14). There are four suprahyoids
and four infrahyoids. Together they flex the head and neck. They
are primarily muscles of some phase of swallowing, but they contract
in cervical flexion whenever the movement is performed against resistance.
By neutralizing one another’s pull on the hyoid bone, their
action is transferred to the head and thence to the cervical spine.
They may be palpated just below the jaw bone.
Hyoid muscles (anterior view).
The fibers of this muscle (Figure 9.15) run diagonally upward
and outward from the lower part of the abdomen, the two muscles
together forming an incomplete letter V, as seen from the front. When
both sides contract, they flex the thoracic and lumbar spine against
gravity or other resistance. When only one side contracts in combination
with other anterior, lateral, and posterior muscles on the same
side, it flexes the spine laterally. When
it combines with other spinal rotators, it rotates the spine to
the opposite side—that is, the right muscle rotates the spine to the left.
External oblique abdominal muscle (obliquus externus
Investigators have found that external obliques show the greatest
activity in movements performed from the supine position such as
forward and/or lateral flexion. Both of the obliques have been
found to increase activity to stabilize the spine in response to
applied loads or to support lower-limb motion. In addition, the
external and internal obliques working together were found to show
activity during a Valsalva maneuver (holding the breath while contracting
the abdominal muscles forcefully). The external oblique may be palpated
at the side of the abdomen.
This muscle (Figure 9.16) lies beneath (i.e., deeper than) the
external oblique. Its fibers fan out from the crest of the ilium,
most of them passing diagonally forward and upward toward the rib cartilages
and sternum, some horizontally forward toward the linea alba, and
some diagonally forward and downward toward the crest of the pubis.
EMG experiments have also shown it to have marked activity in leaning
backward and in decreasing the pelvic tilt from the supine position
during leg raising and lowering (hip flexion/extension).
In summary, the internal oblique flexes
the lumbar and thoracic spine, flexes the spine laterally, and rotates
the spine to the same side. It may be palpated at the side
of the abdomen, below the external oblique. It may also be palpated through
the external oblique when the latter is relaxed, as in rotation.
Internal oblique abdominal muscle (obliquus internus
This is the most superficial of the abdominal muscles (Figure
9.17). It is situated on the anterior surface of the abdomen on
either side of the linea alba. It is a long, flat band of muscle
fibers extending longitudinally between the pubis and the lower
part of the chest. At three different levels transverse fibrous
bands known as tendinous inscriptions cross the muscle fibers. The
muscle is enclosed within a sheath formed by the aponeuroses of
the other muscles making up the abdominal wall. The upper rectus
was found to be more active in exercises involving the upper part
of the body, such as spine flexion from the supine position. The
lower rectus was found to be more active in moments involving a
decrease of pelvic tilt, such as in the supine position bending
the knees and lifting them toward the face until the fifth lumbar
vertebra is raised approximately 5 inches above the supporting surface
(Sarti et al. 1996). In brief, the rectus abdominis flexes the lumbar and thoracic spine, and one side working alone helps flex the spine
laterally. The muscle may be palpated on the front of the abdomen
about 2 or 3 inches from the midline, from the pubis to the sternum.
This muscle (Figure 9.18) is made up of a broad sheet of fibers
that run horizontally from the thoracolumbar fascia and cartilages
of the lower ribs forward to the linea alba. Its primary pull is inward
against the abdominal viscera, hence it is a strong muscle of exhalation
and expulsion. It does, however, help stabilize
the trunk when acts requiring great effort are performed and
may be primarily responsible for the maintenance of intra-abdominal
pressure during lifting. Portions of this muscle are also active
during rotation to the same side; other portions contribute to opposite-side
rotation (Urquhart and Hodges 2005).
Muscles as Spinal Flexors
The rectus abdominis and the external and internal obliques work
together to flex the lumbar and thoracic spine. They play a small
part, however, in flexing the spine from an erect position. This movement
is produced by the force of gravity and controlled by the extensors
in eccentric contraction. The only circumstance that would necessitate
continued contraction of the abdominal muscles would be if the spine
were being flexed against resistance, such as would occur if a person
were lifting a weight by pulling down on a pulley rope and supplementing
arm strength by flexing the spine instead of by the more efficient
method of bending the knees and using the body weight.
The abdominal muscles are markedly active when the spine is being
flexed from a supine position, especially at the beginning of this
movement before the hips start to flex. Their activity is increased
if a weight is held against the chest or on top of the head. (Obviously,
the head and neck flexors are also working hard.) Once the hips
start to flex, the abdominal muscles play a double role—namely,
as movers in flexing the spine and as stabilizers of the pelvis
against the pull of the hip flexors. When a straight spine sit-up
is performed, the abdominal muscles do not act as movers at all.
In this exercise, the trunk as a whole is flexing at the hip joints
on the lower extremities. As the hip flexors are attached to the
movable pelvis, the latter needs to be stabilized against their pull,
and this is done by means of the static contraction of the abdominal
muscles. If the latter are not strong enough to prevent the tilting
of the pelvis, the abdominal action then becomes an involuntary
eccentric or lengthening contraction. If the student is thoroughly
familiar with the attachments of the abdominal muscles, he or she
will know that they cannot be movers in this exercise because they do not cross the hip joints.
The abdominal wall consists of the four abdominal muscles. Together,
these muscles form a strong anterior support for the abdominal viscera.
They are subject to considerable stress from the pressure of the
latter against their inner surface. The more stretched they become,
as in the case of a protruding abdomen, the more heavily the organs
rest upon the abdominal wall, subjecting it to direct gravitational
stress. Thus a vicious circle is set in motion. The pressure against
the lower abdominal wall stretches it still more, causing its protrusion
to increase and subjecting it to ever-increasing gravitational stress.
As is so often the case, correction of this postural fault is much more
difficult than its prevention. A strong abdominal wall is greatly
to be desired.
The abdominal wall acts to stabilize the trunk during extension
and some postural adjustments. Cocontraction of the abdominal muscles
produces an increase in intra-abdominal pressure, which acts to
increase the stiffness of the trunk. Increased trunk stiffness provides
for an increased ability to adjust to loading. Without the stiffness
provided by muscle cocontraction, the spine can tolerate only about
90 N (20 lbs) of compressive load before it buckles (McGill et al.
2003). In many lifting tasks, trunk stiffness is necessary to avoid
undue motion of the individual vertebrae as the result of external
forces. Excessive loading without trunk stability may predispose
one to disc rupture or other injuries of the spine.
These two muscles consist of bands of parallel fibers, slanting
outward as they ascend from their centrally located lower attachments
to their more laterally located upper attachments. The capitis is
much broader than the cervicis. Figure 9.19 clearly shows the left
cervicis and the right capitis muscles. The viewer should try to
visualize both muscles on both sides. When the left and right sides
contract together, they serve to extend
and hyperextend the head and neck. They also help support the
head in erect posture. One side contracting alone can flex the head and neck laterally and also
rotate them to the same side. The muscles may be palpated on
the back of the neck just lateral to the trapezius and posterior
to the sternocleidomastoid above the levator scapulae, especially
if the head is extended against resistance in the prone position
and the shoulders are kept relaxed. It is difficult to identify
Posterior and lateral muscles of cervical spine.
This is a group of four short muscles (Figure 9.20) situated
at the back of the lower skull (occipital bone) and upper two vertebrae
(atlas and axis). It includes the obliquus capitis superior and
inferior and the rectus capitis posterior major and minor. Acting
together on both sides, this group extends and hyperextends the
head. When one side acts alone it flexes
the head laterally or rotates it to the same side.
Suboccipital muscles (posterior view).
The muscle (Figure 9.21) commences as a large mass in the lumbosacral
region but soon divides into three branches.
The iliocostalis branch consists
of lumbar, thoracic, and cervical portions that are named lumborum, thoracis, and cervicis, respectively. It receives
an additional tendon of origin from each rib throughout the thoracic region
and gives off small slips to insert into the ribs in the thoracic
region and into the transverse processes of the vertebrae in the
The longissimus branch consists
of three distinct portions that, in fact, appear to be three separate
muscles (Figure 9.21). Longissimus thoracis is
a broad band lying against the angles of the ribs; longissimus cervicis is narrower and
lies slightly closer to the spine, connecting the transverse processes
of the upper thoracic vertebrae with those of the lower cervical
vertebrae; and longissimus capitis is
a thin strand that lies against the vertebrae for its lower two-thirds
and then slants outward and upward to the mastoid process of the
The spinalis branch lies against
the vertebrae and is attached by separate slips to the spinous processes.
It is of significance in the thoracic region only.
Electromyographic studies have shown that the erector spinae
contributes little to the maintenance of erect posture unless a
deliberate effort is made to extend the thoracic spine more completely
or unless the weight is carried forward over the balls of the feet,
in which case some static contraction of the muscle is required.
In ordinary standing the level of activity is quite low.
In forward flexion from the standing position, the erector spinae
undergoes eccentric contraction until the weight of the trunk is
supported by the ligaments in a flexion–relaxation response.
When the trunk returns from this position, the muscle contracts
concentrically until the body is again erect and balanced. However,
many times the lumbar region of this muscle does not become active
to initiate the return from full flexion and often there are moments
when this muscle is quiet during continued extension.
In almost all vigorous exercises performed from the standing
position, the most active part of the erector spinae was the spinalis
and the least active was the iliocostalis lumborum. The muscle engages
most forcefully in its functions of extension, hyperextension, and
lateral flexion when these movements are performed against gravity
or other resistance. Hyperextension from the prone lying position
while lifting both arms and legs is considered the best exercise
for strengthening the erector spinae (Plamondon et al. 2002).
In brief, when the two sides of the muscle contract with equal
force, the erector spinae extends the head
and spine (assuming that all of its branches are contracting).
When one side contracts alone, especially in conjunction with lateral
and anterior muscles of the same side, it causes lateral flexion.
And when one side alone contracts in a certain precise combination
with lateral and anterior muscles—some on the same side,
some on the opposite side—it rotates the head and spine
to its own side. The lumbar and lower thoracic portions of the muscle
may be palpated in the two broad ridges on either side of the spine.
This group (Figure 9.22) includes the multifidi, rotatores, interspinales,
intertransversarii, and levatores costarum. The latter is primarily
a muscle of the thorax but is included here as a possible assistant
in extension and lateral flexion. These muscles consist of small
slips, in most cases inserting into the vertebrae immediately above
their lower attachments. Some of the fibers run vertically, and
some slant medially as they ascend. The former are best developed
in the cervical and lumbar regions where their action is that of
extension. The latter are best developed in the thoracic region
where they either extend or rotate. It has been suggested that the
muscles in this group are responsible for localized movements. It
seems likely that they also help stabilize the spine. In brief,
acting symmetrically they extend and hyperextend
the spine and acting asymmetrically they rotate
the spine to the opposite side and assist in lateral flexion.
Deep posterior muscles of the spine including part of
the transversospinalis (multifidus, rotators, and semispinalis).
Thoracis, Cervicis, and Capitis
These muscles (Figure 9.23) lie close to the vertebrae beneath
the erector spinae. The thoracis and cervicis portions consist of
small bundles of fibers that slant medially as they ascend to the spinous
processes several vertebrae above. The lower portion of the semispinalis
capitis—that is, the portion starting from the upper thoracic
vertebrae—has a slight medial slant, but the bundles in
the cervical region attaching to the occipital bone are vertical.
Like the muscles in the preceding group, they extend and hyperextend
the thoracic and cervical spine when both sides contract together,
and when only one side contracts they cause lateral
flexion and rotation to the opposite side.
Semispinalis (posterior view), including part of the
transversospinalis (multifidus and rotators).
This is not a different muscle from those already listed but
represents a different organization of the deep muscles of the back.
Some texts use this term for the three spinal muscles whose fibers slant
medially as they ascend, namely the semispinalis,
multifidi, and rotatores (see
Figures 9.22 and 9.23).
Although not a muscle, the thoracolumbar fascia (see Figure 9.18)
is described here because of its importance to the deep muscles
of the spine and erector spinae. It binds these muscles together, holding
them close to the skeletal structure and separating them from the
more superficial muscles of the back. In the lumbar region it curves
around the lateral margin of the erector spinae and folds in front
of it to attach to the tips of the transverse processes of the vertebrae
and to the intertransverse ligaments. Its lateral portion provides
attachment for the transverse abdominis (see Figure 9.18), and its
posterior portion blends with the aponeurosis of the latissimus
dorsi (see Figure 5.14).
Posterior, and Medius
The three scalenes (Figure 9.24) run diagonally upward from the
sides of the two upper ribs to the transverse processes of the cervical
vertebrae. Acting together, they flex the cervical spine and, acting
on one side at a time, they flex the neck
laterally and assist in extension. They also serve to elevate
the upper ribs in forced inspiration. They may be palpated on the
side of the neck between the sternocleidomastoid and the upper trapezius
but are difficult to identify.
The scalenes: anterior, posterior, and medius (anterior
This muscle (Figure 9.25) arises from two heads, one from the
top of the sternum and the other from the top of the clavicle about
2 inches lateral to the first. They unite to attach to bones of
the skull close below and behind the ear. Acting together, they
flex the head and neck. Acting on one side at a time, they flex
the head and neck laterally; they also rotate them to the opposite
side (see Figure 9.27a). They may be easily palpated, as well as
seen, on the side of the neck from just under the ear to the front
of the neck on either side of the sternoclavicular joint.
Muscles that contract to rotate the head and neck to
(Figure 9.19) (Also listed with the Muscles of the Shoulder
Girdle.) When one scapula is fixed, the muscle on that side will
help flex the cervical spine laterally. If both muscles contract
at the same time when both scapulae are fixed, they neutralize each
other without effecting any movement. This action may possibly help
stabilize the neck, especially when the body is in the prone position,
supported on “all fours.”
This flat muscle (Figure 9.26) is situated behind the abdominal
cavity at the side of the lumbar spine. It extends from the crest
of the ilium to the lowest rib and has slips branching medially
to attach to the tips of the transverse processes of the upper four
lumbar vertebrae. Acting bilaterally, it is credited with stabilizing
the pelvis and lumbar spine. Acting unilaterally, it flexes the
lumbar spine to the same side (lateral flexion). In a 1972 EMG study,
Waters and Morris found that together with other posterior spinal
muscles, as well as with the abdominal muscles, it contracted regularly
in each cycle of walking. According to the electromyogram reproduced
in Muscles Alive (Basmajian and DeLuca
1985), its action appears to coincide with the moment of heel contact. The
muscle may be palpated on a thin, muscular subject just lateral
to the erector spinae in the lumbar region.
Quadratus lumborum (posterior view).
(Also listed with the Muscles of the Hip) Like the quadratus
lumborum, the psoas (see Figure 7.14) is situated at the back of
the abdominal cavity. Together, these two form the posterior abdominal
wall. Although the psoas is primarily a muscle of the hip joint,
its action on the lower spine and pelvis is of interest. Because
the psoas major muscle at its promixal end attaches to the sides
of the bodies to the front and lower borders of the transverse processes
of all the lumbar vertebrae, it has been thought to be a mover of
the lumbar portion of the spinal column.
Although there appear to be diverse opinions regarding such muscular
actions, it seems likely that the differences are not of great importance.
Frequently, when there is lack of agreement regarding movement,
one may safely assume that the true function of the muscular contraction,
with reference to the joints in question, is more likely to be stabilization
or balance than purposeful movement. In their edition of Brunnstrom’s Clinical Kinesiology, Lemkuhl
and Smith (1983) described this type of action with unusual clarity.
They liken the muscles that are situated near the spinal column
(erector spinae, psoas major, and so on) to guy ropes supporting
an upright pole. When the pole starts to tip, the tension of the
ropes on the opposite side increases. In like manner, if a person
starts to lean backward, possibly to favor weak posterior muscles,
the muscles on the front of the spine spring into action. Thus it
would appear that the most important role of the psoas is stabilization or balancing of the spine in
response to other forces acting on the latter. In addition, unilateral
contraction contributes to lateral flexion of
the lumbar spine.