DRM411H1 Study Guide - Lumbar Vertebrae, Plumb Bob, Thoracic Vertebrae

Centre for Drama, Theatre and Performance Studies
Course Code
David Roberts

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Alyssa Dority
Chapter Thee- The Spine/Plumb Line:
Ideal Standing Postural Alignment:
o Ideal posture encompasses a balance of these sagittal curves and a positioning of joints so that
the body’s line of gravity is located in the median plane and runs in front of the thoracic
vertebrae and just anterior to or through S2 (figure 3.23a in text)
o This gravity line would ideally pass through or close to the centers of key weight bearing joints
so that the undue joint stress is avoided and minimal muscular contraction is required to
maintain the desired position
o Positioning of the line of gravity allows much of the necessary support of the spine to be
provided by intervertebral disc pressures and constrains offered by ligaments, fascia, and
capsules of the facet joints
o Slight additional active support is often provided by low levels of activity of the spinal extensors
(particularly the thoracic extensors and deep posterior spinal group) and the abdominals
(particularly the internal oblique)
o As the gravity line continues downward, it runs slightly posterior to the axis of the hip joint with
the resulting tendency for hip extension (extensor moment) limited by the iliofemoral ligaments
and in some cases, slightly activity of the iliopsoas muscle; just anterior to the axis of the knee to
extend (extensor moment) limited by passive constrains (posterior to the knee capsule and knee
ligaments); and just anterior to the ankle axis, generally requiring a low levels of activity in the
calf muscles (particularly the soleus) to prevent the body from falling forward
o To conceptualize the ideal postural alignment, the vertical gravity line is reflected by a plumb
line and surface landmarks on the body are used to reflect where this gravity line would actually
run inside the body
o A plumb line is a cord with a weighted (plumb bob) attached to its distal end so that when hung
it will provide an absolute vertical line as a reference for measuring deviations
o Any landmarks that do not fall upon the plumb line would reflect deviations from the ideal
alignment; assuming that the shoulders are not “rolled”, having all of these landmarks aligned
along the plumb line generally indicates a very basic correct balance of the sagittal spinal curves
o With ideal alignment, the pelvis is vertical (ASIS in a vertical plane with the pubic symphsis)
rather than tilted forward or backward
o The positioning of the pelvis will directly affect the spinal alignment, as an anterior pelvic tilt
tens to increase the lumbar curve while a posterior pelvis tilt tends to decrease the lumbar
o The position of the spine therefore effect the alignment of the lower extremities; ex.
Hyperextended knees
o When looking at a dancer from behind, the gravity line should be:
Gravity line should bisect the distance between the heels and
Ideally be in line with the spinous processes of the vertebrae
o When looking at a dancer from the front, the gravity line should be:
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Alyssa Dority
Bisect the distance between the feet and
Ideally be in line with midline structures such as the pubis symphsis, umbilicus and nose
o These views allow to see if there is asymmetry between the right and left side s of the body
(such as scoliosis)
Lumbar Hyperlordosis:
o Lumbar lordosis is a term to describe large lumbar curvature (ex bending backwards)
o Lumbar hyperlordosis is a more accurate term and describes an increasing inclination of the
sacrum, anterior pelvic tilt and sometimes forward displacement if the torso relative to the ideal
postural plumb line
o Lumbar hyperlordosis is not only aesthetically undesirable but also may increase the risk for
lower back injury
It increases the tendency for the lower vertebrae to slide forward on the underlying
vertebrae (shear force)
This increased shear produces extra stress on many spinal structures (stress fractures)
o Fixed hyperlordorsis is associated with greater contraction of the erector spinae, which may
allow low back muscle fatigue and strain to occur more readily
o This is preventable in young dancers; as they are forcing turnout
It may decrease with years of training, but not always and it harder to fix when older
o To prevent:
Strengthen abdominal muscles (determining distance between ribs and pelvis; therefore
affecting the curvature of the lower spine and hence ideal alignment)
Stretch of hip flexor and lower back ( as low back and hip flexor tightness; commonly
from growth spurts in adolescence)
One should also test for the hip flexor range of motion (just to be safe )
o Many dancers with hyperlordorsis appear to exhibit excess back extensor activation, and
successful change in this posture for standing and dynamic movement often involves greater co-
activation of the abdominal muscles and upper back muscles extensors for correct positioning
and spinal stabilization
In an effort to achieve this, dancers “pull up” the pubic bone, so that it is in line with the
ASIS, achieving neutral alignment
Some dancers who have lumbar hyperlordorsis or excessively extend the spine higher
up tend to displace the lower ribs forwards
These dancers need to focus on bringing the ribs back down/back
Cueing to knit the front of the pelvis and rib cage closer together while still maintaining
a lift along the central plumb line or lift the upper back can be sometimes effective
o Kyphosis is characterized by an abnormal increase in the thoracic curvature (humpback)
o This excessive curvature can be rigid in nature as a consequence of various diseases or structural
abnormalities, while in other cases it is more flexible and functional in nature
The functional version is seen more in sedentary individuals, who sit in slumped posture
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