The Spine 117
of concern because of the increased stress it creates
within the discs. One study reported that intradiscal
pressure at L3 doubled in magnitude with 40° of
forward bending (Nachemson, 1981).
A different concern becomes operative with
extreme degrees of forward bending. After about
50° of forward bending, the activity of the spinal
extensors actually decreases instead of increasing,
until at full flexion these muscles are inactive; this
is termed the flexion relaxation phenomenon (Hall,
1999). In this position of full flexion, the spine is
devoid of the stability and protection provided by
muscular contraction and relies on passive support
from the joint capsules and ligaments, discs, thora-
columbar fascia, and the passive elastic components
of the back extensors. This is potentially dangerous
for these passive constraints, particularly given that
they are susceptible to fatigue. For example, with
repetitive loading, discs appear to lessen their ability
to absorb shock or withstand forces, and injury can
then result from relatively small forces. In addition,
the tension in the interspinous ligament associated
with full flexion can increase facet joint loading and
anterior shear force (Hall, 1999). These observations
have led to recommendations to use full flexion with
care and that adding large forces to this vulnerable
position such as those associated with percussive toe
touching or bounce stretching is not advisable in
recreational athletes.
However, many dancers find roll-downs and such
inverted positions helpful for developing flexibility,
reducing excessive low back tightness, and finding
certain neuromuscular connections. One approach
is to use such spinal flexion in dance populations
prudently (avoiding excessive use in terms of dura-
tion of holds or number of consecutive repetitions)
when the body is adequately warmed and with careful
attention to technique. In terms of technique, poten-
tial risks can theoretically be lessened by emphasizing
keeping the head close to the torso as the dancer
flexes the spine (decreasing the moment arm of
the resistance) and by emphasizing tightening the
abdominals and pulling them in toward the spine to
help reduce shear forces and protect the spine via
intra-abdominal pressure or thoracolumbar fascia
tensioning. Also, inadequate hamstring flexibility
will not allow adequate forward rotation of the pelvis,
which occurs after about 45° of spinal flexion (see
FIGURE 3.38 Specific co-contraction of the abdominal muscles and spinal extensors to limit hyperextension in the
low lumbar spine and emphasize upper back extension. (A) Incorrect technique, (B) correct technique.
AB
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