A pelvis-oriented margin of stability is robust against deviations in walking direction.

The Margin of Stability (MOS) is often assessed relative to the intended, linear path of walking progression. When an unanticipated or irregular change in direction occurs, such as during a sudden turn or during activities of daily living, distinguishing the lateral from anteroposterior MOS can be challenging. The purpose of this study was to assess an anatomically orientated method of calculating the MOS using the pelvic orientation to define lateral and anteroposterior directions. We hypothesized that when straight walking was disrupted with a curved path, the pelvis-oriented MOS measure would be less variable compared to the global-oriented MOS measure. We recruited 16 unimpaired participants to walk at preferred and fast walking speeds along a straight walking path, as well as a path with an exaggerated, curvilinear deviation. We determined the within-subject mean and standard deviation of the anterior MOS at mid-swing and the posterior and lateral MOS at ipsilateral foot strike. For straight walking and curved walking separately, repeated measures factorial ANOVAs assessed the effects of model (global or pelvis-oriented), limb (left or right), and speed (preferred or fast) on these MOS values. Based on reduced variability during curved walking, the pelvis-oriented MOS was more robust to walking deviations than the globally defined MOS. In straight walking, the pelvis-oriented MOS was characterized by less lateral and more anterior stability with differences exacerbated by faster walking. These results suggest a pelvis-oriented MOS has utility when the path of progression is unknown or unclear.