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

This experiment analysed the spinal shrinkage due to repetitive exertions c onfined to each of three separate axes (twist, lateral bend, flexion). Whil e the experiment was performed twice with small technique modifications in the twisting task (and thus two data collections were performed), the essen tial 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 a xis 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 demonstra ted significant spinal shrinkage (1.81 and 3.2 mm in the two experiments) b etween the pre- and post-stature measurements while no clear effect emerged for the other two tasks. These data suggest that repetitive torsional moti ons impose a larger cumulative loading on the spine when compared with cont rolled lateral or flexion motion tasks of a similar moment.