118 Dance Anatomy and Kinesiology
Lumbar-Pelvic Rhythm on p. 183 for more informa-
tion) and can result in increased stress to the lumbar
spine (Hamill and Knutzen, 1995; Plowman, 1992).
Dancers with tight hamstrings can modify such a posi-
tion to reduce back stress by slightly bending the knees
or supporting the torso with forearms on the thighs
until adequate hamstring flexibility is developed.Partnering
Partnering other dancers is associated with very large
forces, but the potential risk to the spine can be
lessened by appropriate spinal and pelvic alignment
of the lifter, specific muscle emphasis during lifting,
appropriate positioning of the partner, and adequate
strength and flexibility in key muscles. In terms of
alignment, emphasis on lifting with the legs with the
torso more vertical is associated with lower forces
borne by the spine than bending the spine forward
and “lifting with the back.” The intradiscal pressure
at L3 has been estimated to be about 382 pounds
(173 kilograms) of force when one is picking up a
22-pound (10-kilogram) weight with the back straight
and knees bent, versus 427 pounds (194 kilograms)
when bending forward with the back (Nachemson,
1981). Considering that another dancer is likely to
weigh five or six times more than the weight used in
that study, such a change in load to the discs could bevery meaningful. Similarly, the degree of rotation can
markedly influence spinal stresses. Some structures
of the spine such as the discs are vulnerable to rota-
tion, and most back injuries involve a combination of
flexion and rotation or hyperextension and rotation.
During lifting of that same 22-pound weight, rotating
20° with the spine flexed 20° increases intradiscal
pressure to 472 pounds (214 kilograms) of force. Fur-
thermore, asymmetrical positioning has been shown
to negatively affect the ability to lift heavy loads, with
losses of 12%, 21%, and 31% at 30°, 60°, and 90° of
asymmetry, respectively (Caillet, 1996).
Even more dramatic in determining stresses to the
spine is the distance the partner is from the spine.
Having a dancer farther away from your body will
greatly increase the resistance torque that must be
overcome by the shoulder muscles and the bending
torque that must be met by the trunk muscles to
maintain a stable position. Studies have shown that
whether one is lifting with the torso erect or bent
forward, the farther the weight is from the body the
greater the activity of the spinal extensors and the
greater the pressure borne by the discs (White III
and Panjabi, 1978). The calculation in one study was
that lifting a 100-pound (45-kilogram) weight with
the weight about 30 inches (76 centimeters) in front
of the fulcrum (L-S disc) and the legs straight would
require 1,500 pounds (680 kilograms) of muscle“Lift the Upper Spine Up and Back”
T
he cue to “lift the upper spine up and back” can be interpreted anatomically as focusing on extend-
ing the thoracic spine backward without letting the rib cage go forward. Focusing on “pulling up”
with the inferior attachment of the abdominal muscles onto the pelvis will help limit anterior tilting
of the pelvis and resultant undesired excessive hyperextension in the lower lumbar vertebrae. Then,
focusing on arching the mid and upper thoracic spine such that the sternum lifts up and back will
help achieve the desired distribution of some of the arch to higher regions of the spine. However,
achievement of this desired arch requires very subtle co-contraction of the abdominal muscles and
back extensors in very specific regions of the spine.
For example, excessive use of the spinal extensors in the lower thoracic and upper lumbar region
will tend to create undesired forward movement of the anterior rib cage. In contrast, excessive
stabilization of the rib cage by the abdominal muscles and holding the ribs down will not allow the
thoracic spine to hyperextend. Thus, while a consistent “pulling up” of the lower attachment of the
abdominal muscles onto the pelvis is maintained, the upper attachment of the rectus abdominis and
obliques onto the rib cage must be allowed to move away as the sternum lifts up and back, so that the
abdominal muscles are used eccentrically to help control backward movement of the trunk while the
spinal extensors (particularly the thoracic) are used concentrically to cooperatively create the desired
positioning of the spine as seen in figure 3.38B.