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Introduction: This study examined the effects of wearing
an abdominal belt (elastic back support) and the rise in intra-abdominal
pressure on the lumbar spine stability. Increase in lumbar pressure
is hypothesized to increase lumbar spine stability.
Methods: Ten subjects in their mid-twenties to early
thirties were placed in a jig in a semi-seated position. Hip
motion was restricted while the upper torso remained free to
move in any direction. They were instructed to pull on a cable
which was held at one end by a chest harnesss attachment at the
T9 level. The distal end of the cable was attached to a release
mechanism by an electro-magnet. The subjects had a transducer
introducer, to monitor IAP, introduced into their stomachs in
the usual manner. IAP levels were monitored on an oscilloscope
with readings in full view of the subjects. The subjects were
shown the valsalva maneuver method of controlling IAP. When the
IAP target level was reached, an operator released the electro-magnet,
providing a "quick release" of the resistance. Quick
releases were performed in conditions of trunk extension, trunk
flexion and lateral bending (35% of maximum.) Trials were performed
at 0%, 40% and 80% of the individual's maximum IAP in each direction.
Only the 0% and 80% IAP trials were repeated while wearing a
standard 10cm wide nylon belt (back support).
Results: Flexion trunk stiffness increased by 21% in
the belt (back support) intervention at 0% IAP levels. During
lateral bending, trunk stiffness increased by 30% at IAP levels
of 80%. With no IAP, the trunk stiffness increased by 29% and
9% in flexion and lateral bending, respectively. The effects
of IAP and belt (back support) conditions were additive in both
directions. Combined effects of wearng an abdominal belt and
the increased IAP level to 80% of maximum provided 83% and 86%
more trunk stiffness in flexion and lateral bending respectively.
Results in extension druing this study on trunk stiffenss lacked
statistical significance.
Discussion: It is likely that increase in spine stability
due to IAP was gained from the concomitant increase in muscle
coactivations needed to generate IAP.
Trunk stiffening due to just the belt (back support) is likely
a passive mechanism stemming from the wide and stiff belt placed
between the rib case and pelvis. These findings are relevant
to low back injury prevention and rehabilitation strategies.
Increased spine stability may provide greater protection against
injury following unexpected or sudden loading.
"The results indicated that both wearing an abdominal
belt and increased IAP can each independently, or in combination,
increase trunk stiffness, and therefore, increase lumbar spine
stability under sudden loading conditions."
Proceedings of NACOB 98. The Third North American Congress
on Biomechanics, Waterloo, Canada, August 14th- 18th, 1998.
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