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unknown user
03-08-2001, 08:18 PM
Dear Subscribers:

What is the maximal spinal shrinkage (reduction in stature) that a person
could experience without injury? How short can we get?

There is a considerable number of studies reporting changes in body height
(spinal shrinkage) during physical activity, different work-loads and
circadian variations (e.g., Althoff; Boocock; Reilly; Van Dieen, etc).
However, there is no reference to the maximal shrinkage a person could
withstand without injury.

One attractive way of doing this could be extrapolating the nmechanical
behaviour of a single intervertebral disc examined in an "in vitro"
condition. In this case, it would be necessary to assume that all
intervertebral discs (i.e., cervical, thoracic, lumbar discs) behave in a
similar manner, i.e., they lose height proportionally to their initial height
(a normalised value e.g., X% of their unloaded/resting condition). So, by
replacing all intervertebral discs by one large disc (i.e., representing the
height of all intervertebral discs together) and knowing the maximal
deflection that occur within the elastic zone of the disc, changes in the
whole spine could be estimated if we assume that the intervertebral discs
constitute approximately 30-33% of the entire spine.

However, I found difficult to predict the maximal "theoretical" shrinkage
using the literature as reference. In most experiments, where the discs were
exposed to axial compressive loads, only the absolute change in disc height
was reported (e.g., Virgin, 1951; Kazarian, 1975). Perhaps, the reason for
this is because most studies preserve the intervertebral discs attached to
the adjacent vertebras (for clamping the specimens) and do not quantify the
disc height before testing (initial, unloaded condition).

Please, during this discussion disregard that all changes that may occur in
the appendicular skeleton and assume that all changes in the height of the
spine occurs in the intervertebral discs.

Any reference in the literature I may have missed that could clarify this?
Any comments?

I thank you in advance

Andre Rodacki
Department of Exercise and Sport Sciences
Manchester Metropolitan University
Hassal Road, Alsager, Staffordshire
United Kingdom
ST7 2HL

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