Understanding how people modify their stepping to maintain gait stability may provide information on fall risk and help to understand strategies used to reduce loss of balance. The purpose of this study was to identify the stepping strategies healthy young individuals select to maintain balance while walking on a destabilizing surface in various directions. A treadmill mounted on top of a 6 degree-of-freedom motion base was used to generate support surface oscillations in different degrees of freedom and amplitudes. Fifteen healthy young adults (21.3 ± 1.4 years) walked at self-selected speeds while continuous sinusoidal oscillations were imposed to the support surface in a one degree of freedom: rotation or translation in the mediolateral (ML) direction and rotation or translation in the anteroposterior (AP) direction, with each condition repeated at three different amplitudes. We compared step width, length, and frequency and the mean and variability of margin of stability (MoS) during each experimental walking condition with a control condition, in which the support surface was stationary. Subjects chose a common strategy of increasing step width ( p < 0.001) and decreasing step length ( p = 0.008) while increasing mediolateral MoS ( p < 0.001), particularly during oscillations that challenged frontal plane control, with rotations of the walking surface producing the greatest changes to stepping.

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While devices which allow scientists to perturb normal walking are becoming increasingly common, postural adaptations to these perturbations have not been fully quantified. One way to quantify postural responses to perturbations are through the assessment of variability of step length and width. In the present study we determined variability of both step length and width while subjects walked under perturbations of varying amplitude in roll, pitch, yaw, anteroposterior, lateral, and combined roll, pitch, yaw directions. Step kinematics were quantified using motion analysis. The majority of changes in step length variability occurred in Pitch (p<;0.01), mediolateral (p<;0.05) and anteroposterior (p<;0.01) directions. Changes in step width variability were most apparent in combined Roll-Pitch-Yaw (p<;0.01) as well as Roll (p<;0.05), and Yaw (p<;0.05) directions. These data demonstrate that sinusoidal perturbations while walking on a treadmill are sufficient to disrupt normal postural control. These conditions therefore may be useful in constructing rehabilitation programs to improve dynamic balance.