Spinal shrinkage during repetitive controlled torsional, flexion and lateral bend motion exertions

This experiment analysed the spinal shrinkage due to repetitive exertions confined to each of three separate axes (twist, lateral bend, flexion). While the experiment was performed twice with small technique modifications in the twisting task (and thus two data collections were performed), the essential components were as follows. A total of 20 subjects were loaded with an equal moment of 20 Nm in each of the three axes, on 3 separate days (one axis per day). Subjects performed each task for 20 min at 10 repetitions min(-1), where stadiometer measurements of standing height were taken prior to and immediately following the 20 min exertion. The twisting task demonstrated significant spinal shrinkage (1.81 and 3.2 mm in the two experiments) between the pre- and post-stature measurements while no clear effect emerged for the other two tasks. These data suggest that repetitive torsional motions impose a larger cumulative loading on the spine when compared with controlled lateral or flexion motion tasks of a similar moment.