Posture And Gait:
Kinesiology Application To Motion
Men and women have different centers of gravity and thus differ in
their natural posture stances.
During evolution, perhaps the most important changes to occur in the
spine was the ability to stand erect or biped. In order to become
erect, there has to occur approximately 30° anterior inferior tilt
of the sacrum in the upright posture creating a natural lumbar
lordosis. Because of this phenomenon, the mass of the gluteus
maximus developed to a size unique to man that also necessitated a
concurrent size increase of the quadriceps muscle.
In standing, establishing a stable base at the foot and the ankle
are important. Although many muscles can produce tension to maintain
a relative equilibrium, most research studies agree that the soleus
muscles is primarily responsible more so than the gastrocnemius,
tibialis anterior, peroneus, or the tibialis posterior muscle.
Physiologically as a slow twitch muscle, the soleus can remain
active for long durations of time.
In the pelvis area, the sacroiliac joints are responsible for
balancing of weight transmitted between the spinal column and the
lower extremities. The sacrum that is wedged between the two ilia
normally experiences little movement. Upright posture however has a
tendency to rotate the sacrum forward and downward.
In sitting postures, the spine angle to the pelvis was evaluated and
found that without any back supports the spine has the least amount
of stress when the lumbar spine to the pelvic angle is 135°. As a
result, there were new designs in chairs that had no back that
tilted the seat downward and supported the lower leg to accommodate
this 135-degree angle. However, in the case where the low back had
some type of lumbar support the smallest strain on the back with
natural posture occurred with an incline of a 120 degrees of spine
Anteroposterior tiling of the pelvis exerts significant influence on
the primary curves of the spinal column. Excessive downward pelvic
tilting is found in individuals who developed contracture of the
iliopsoas muscle, necessitating for increased curvature of the
thoracic spine as a compensatory mechanism.
Muscular deficiencies can also produce deficits that have postural
implications. The most serious in the lower limb injuries involve
the posterior calf muscles, the quadriceps, and the hip extensors.
If the plantar flexors are lost, maintaining balance also becomes a
problem. Quadriceps insufficiency creates a little difficulty during
standing because the center of rotation of the knee is posterior to
the line of gravity.
Motion of the pelvis is critical for normal locomotion. The pelvis
has been shown to rotate approximately 11.5° advancing anteriorly on
the side of the limb swinging forward. During the stance phase, the
hip abductors must be active in order to prevent the opposite side
of the pelvis from dropping. The upper trunk rotates in the opposite
direction of the pelvis in order to maintain a balanced mechanism.
As the lower limb is advanced, the contralateral arm moves forward.
The shoulder flexion and extension during this motion is 32 degrees.
Muscular activity with gait involves the gluteus maximus, rectus
femoris, vastus muscles, and hamstrings to control the extension
moments required at the hip and knee. The abductor group is not
required to control movements but are found to be active during the
gait cycle. For abduction and adduction, the most significant
movement involves hip abduction. This movement is consistent with
contraction of the gluteus medius and minimus and the institution of
the abductor mechanism that accomplishes elevation of the
contralateral side of the pelvis.
Using engineering methodology in determination of joint torque to
calculate joint arthrosis it was found that the greatest component
of joint force acts vertically. Similar patterns exists all lower
Control of the trunk can be considered from either the viewpoint of
flexors versus extensors or by the way of regions of the spine. The
categorizing of flexors versus extensors provides the ability to
categorize the musculature functionally while categorizing them by
regions of the spine allows for important regional differences. In
describing the posterior musculature of the lumbar spine, the
deepest layer is the erector spinae group. The intermediate layer is
the serratus posterior inferior, and the most superficial layer is
the latissimus dorsi. All these muscles are important in the
extension of the lumbar spine as well as the ability to increase
The posterior muscles of the neck are much more complex. The deepest
layer contains the suboccipital muscles. The next layer includes the
semispinalis, capitis, and cervicis. The splenius and levator
scapulae are just beneath the superficial plane. The trapezius and
sternocleidomastoid muscles are the most superficial plane muscles.
A muscle of interest is the psoas muscle. This muscle extends from
the upper lumbar spine anteriorly, transversing through the pelvis
and attaches in the lesser trochanter of the femur. This muscle has
a complex function due to its multiple segment attachments.
Furthermore, this muscle is draped over the anterior rim of the
pelvis, which provides a mechanism for altering the position of the
pelvis. Because upward and downward tilting of the anterior rim of
the pelvis is directly related to the degree of respective flexion
and hyperextension in the spine, the effect of this psoas muscle on
the lumbar spine can be dramatic. The patient who has tightness of
the psoas muscle will pull the anterior rim anteriorly creating an
anterior pelvic tilt. Such tilt causes the sacrum to be inclined
further forward, which in turn positions the fifth lumbar vertebrae
more anteriorly. The result of this is increased lumbar lordosis.
To counteract the anterior tilt, it is important to strengthen and
utilize the abdominal muscles, notably the rectus abdominis and the
external obliques. In standing, the internal obliques were more
active than the external obliques with little activity in the rectus.
The function of the abdominal muscles during exercise provides an
effective means of strengthening the anterior abdominal wall. The
highest levels of rectus abdominis activity occurred during the
sit-up performed in the hook lying position.
Taras V. Kochno, M.D.
Board Certified in Physical Medicine & Rehabilitation
Copyright July 2, 2012