Length of the spine while sitting on a new concept for an office chair.

Changes in spinal length were used to evaluate a new concept for an office chair. This so-called dynamic chair imparts passive forced motion to the seated subject. The passive forced motion is a rotary movement about an axis, perpendicular to the seat with amplitude of 0.6 degrees and a frequency of 0.08 Hz. Change of stature is assumed to provide a measure for spinal load. Eight subjects were measured in two situations: static (without motion) and dynamic. In both situations the same office tasks were performed and the duration of the sitting period was 1 h. To allow for the normal shrinkage curve the starting time was the same on each of the measurement days. The results indicated a significant difference: when sitting on the dynamic chair the average spinal length increased in comparison to the spinal length in the static chair, where average spinal length decreased. It was concluded that there is spinal distress relief due to the passive motion of the chair.