Dance Anatomy & Kinesiology

116 Dance Anatomy and Kinesiology

itself can occur (spondylolysis). Activities such as

dance that utilize repetitive hyperextension tend to

display increased incidence of low back injury, and so

an understanding of this movement is important.

Undesired hyperextension can occur statically

as part of standing posture (lumbar hyperlordosis)

or dynamically in dance movements such as when

one is rising from a plié, laterally flexing the spine,

jumping, or turning. As just described, an important

part of dance training is to develop the desired spinal

alignment such that this undesired hyperextension is

avoided. However, in other cases such as an arabesque

jazz layout or various porte de bras movements involv-

ing arching to the back, spinal hyperextension is a

necessary component of the dance movement. In

such cases, the potential for associated injury can

be reduced with appropriate co-contraction of the

abdominal muscles and back extensors, so that the

amount of hyperextension and shear stress in the

low lumbar spine is limited and greater emphasis is

placed on arching higher and throughout more of

the back (figure 3.38). Since tremendously more

hyperextension is naturally allowed in the lumbar

than the thoracic spine, this technique

requires the development of high levels of

abdominal and upper back strength, upper

back flexibility, and subtle neuromuscular

coordination that can take years to develop.

Technique cues that can be used to help

obtain this arch include (1) imagine arching

up and back over a barrel; (2) imagine that

someone is lifting you up and back from just

below the shoulder blades, and the scapulae

become a shelf to support the upper back;

(3) think of the spine as a flexible column

with the goal to create a continuous long

arc rather than allowing the lower portion

to collapse and crimp.

Spinal Forward Flexion

Movements involving forward flexion of

the spine are very common in modern

and jazz dance forms and may relate to

the disc injuries more commonly seen in

older modern dancers. In contrast to what

occurs with hyperextension, with forward

flexion the anterior portions of the vertebrae

press toward one another and the posterior

structures of the spine tend to pull away from

one another. This creates compression at the

front of the disc and tension at the back of the

disc and increases intradiscal pressure. It also

creates large stresses on the ligaments that

span between adjacent vertebrae posteriorly. Further-

more, during flexion the top vertebrae tends to slide

forward as it tilts due to the weight of the trunk. This

sliding tendency creates large shear forces. Lastly,

muscle activity influences spinal stresses.

In terms of the influence of muscles, the activity

of the back extensors initially increases the further

the spine bends until about 40 to 50° of spinal

flexion (Andersson, Ortengren, and Nachemson,

1977). This is the case because the head and torso

are moving farther away from the axis of rotation

of the spine (increasing the moment arm of the

resistance), and so greater force must be generated

by the spinal extensors to eccentrically counter this

torque and prevent uncontrolled falling of the torso.

This greater force is of concern in terms of straining

the back extensors, and muscle endurance has been

shown to be adversely affected by greater degrees of

flexion. For example, the length of time in which

workers were able to maintain a position was reduced

from 13 minutes with 20° of forward flexion to 4

minutes with 30° of forward flexion (Soderberg,

1986). The greater force of the back extensors is also

FIGURE 3.37 Spinal alignment during lateral flexion. (A) Balanced

muscle co-contraction resulting in desired spinal alignment, (B) inad-

equate abdominal contraction resulting in undesired spinal align-

ment.

AB