Measurement of time-dependent height-loss during sitting.

The application of a static load causes the spine to deform with time, that is to say the spine 'creeps'. This phenomenon has been measured in vivo as a change in body height. Fifteen females within three different age groups were exposed to repeated five minute sessions of sitting, during which the shrinkage of the spine was measured continuously. All the subjects demonstrated shrinkage during these exposures. A trend towards increased shrinkage in the oldest group was observed and statistical differences on initial shrinkage were also noted. These findings were contrary to those observed in some other studies, but were, however, in agreement with recent in vitro studies. Apart from the aim of studying differences in 'creep' behaviour between subjects of different ages, the endeavour was to improve the technique so as to measure the continuous change in height due to a certain static load.