Shrinkage as a measure of the effect of load on the spine.

A new method for measuring spinal load is proposed, whereby changes in body height are used as a measure of disc compression. The rate and magnitude of disc compression are caused by the loading and its temporal pattern. A device is reported for measuring body height (SD less than 1 mm). Experiments showed the dinural shrinkage during a working day and the rapid recovery when lying down. Other experiments demonstrated how the rate of shrinkage is a function of the load on the spine. Further, shrinkage when sitting in different chairs has been compared, and the results are in agreement with disc pressure measurements, reported in the literature. Finally, examples are given of how the method can be used in ergonomic evaluations.