Axial pelvis range of motion affects thorax-pelvis timing during gait.
During gait, patients with pelvic girdle pain and low back pain demonstrate an altered phase relationship between axial thorax and pelvis rotations (thorax-pelvis relative phase). This could be the result of an increase in axial pelvis range of motion (ROM) which has been observed in these patients as well. To establish this relationship, we investigated if altered axial pelvis ROM during gait affects thorax-pelvis relative phase in 12 healthy subjects. These subjects walked on a treadmill and received real-time feedback on axial pelvis rotations. Subjects were asked to (1) walk normal, and walk with (2) decreased and (3) increased pelvis ROM. Gait speed and stride frequency were matched between trials. Subjects were able to increase pelvis ROM to a large extent, but the reduction in pelvis ROM was relatively small. Walking with large pelvis ROM resulted in a change in thorax-pelvis relative phase similar to that in pelvic girdle pain and low back pain. A forward dynamic model was used to predict the effect of manipulation of pelvis ROM on timing of thorax rotations independent of apparent axial trunk stiffness and arm swing amplitude (which can both affect thorax-pelvis relative phase). The model predicted a similar, even larger, effect of large axial pelvis ROM on thorax-pelvis relative phase, as observed experimentally. We conclude that walking with actively increased ROM of axial pelvis rotations in healthy subjects is associated with a shift in thorax-pelvis relative phase, similar to observations in patients with pelvic girdle pain and low back pain.