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  • How short can we get?

    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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