Dynamic stability and stepping strategies of young healthy adults walking on an oscillating treadmill

Abstract

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.

Fig 1. Experimental equipment.

(A) Subjects walked on a treadmill mounted on top of a 6 degree-of-freedom motion base. (B) Examples of the degrees of freedom the motion base can move.

Fig 2. Step parameters.

Step frequency (A), step width (B) and step length (C) for all walking conditions are shown for following conditions: control walking condition (C), roll, pitch, yaw combination (RPY), pitch (P_L, P_M, P_H), roll (R_L, R_M, R_H), mediolateral (ML_L, ML_M, ML_H) and anteroposterior (AP_L, AP_M, AP_H) oscillations at low (L), medium (M) and high (H) amplitudes. Asterisks represent significant difference (p < 0.05) with respect to the control condition.

Fig 3. Dynamic stability.

The mean MoS_ML (A) and the coefficient of variation of MoS_ML (B) are shown for following conditions: control walking condition (C), roll, pitch, yaw combination (RPY), pitch (P_L, P_M, P_H), roll (R_L, R_M, R_H), mediolateral (ML_L, ML_M, ML_H) and anteroposterior (AP_L, AP_M, AP_H) oscillations at low (L), medium (M) and high (H) amplitudes. Asterisks represent significant difference (p < 0.05) with respect to the control condition.