Balance and recovery on coronally-uneven and unpredictable terrain.

Stepping on coronally-uneven and unpredictable terrain is a common gait disturbance that can lead to injurious falls. This study identified the biomechanical response to a step on coronally-uneven and unpredictable terrain through observation of participants traversing a walkway with a middle step that could be blinded to participants, and positioned either 15° inverted, 15° everted, or flush. The isolated disturbance was intended to simulate stepping on a rock, object, or other transient coronal disturbance and allow for observation of the subsequent balance recovery. Gait balance was affected by the disturbance, and was measured by the range of coronal whole-body angular momentum, which compared to unblinded flush, increased during blinded eversion, and decreased during blinded inversion. Analysis of external coronal moments applied to the body about the center-of-mass by the disturbed and recovery legs suggested the disturbed leg contributed more to differences in the range of coronal angular momentum, and thus more to balance recovery. The stepping strategy for the disturbed and recovery steps was measured by mediolateral foot position, and appeared to have been mostly affected by anticipatory actions taken by participants before stepping on the blinded terrain, and not by the terrain angle. In contrast, on the disturbed step, distinct differences between blinded inversion and eversion in the coronal moments of the hip and ankle suggested the hip and ankle joint moment strategies were important for adapting to the terrain angle. A clinical implication of this result was interventions that augment these moments may improve gait balance control on coronally-uneven and unpredictable terrain.