Dynamic Gait Stability, Clinical Correlates, and Prognosis of Falls Among Community- Dwelling Older Adults  Tanvi Bhatt, PT, PhD, Debbie Espy, PT, PhD, Feng Yang, PhD, Yi-Chung Pai, MPT, PhD  Archives of Physical Medicine and Rehabilitation  Volume 92, Issue 5, Pages 799-805 (May 2011) DOI: 10.1016/j.apmr.2010.12.032 Copyright © 2011 American Congress of Rehabilitation Medicine Terms and Conditions

Fig 1 (A) Shown is a schematic diagram of the experimental set-up with the approximate position of the participant at touchdown of the slipping (right) limb. The unfilled circles indicate positions of passive-reflective markers on the body segments and movable platform. The solid (right side) and dotted (left side) gray lines joining the markers represent the body-segment links used to calculate the whole body COM. The I-beam and safety harness system are much higher than shown (9m above the ground). Shown are the 2 sliding devices that were placed side-by-side to induce the bilateral slips. The low-friction, nonmotorized moveable top plates (right and left) were mounted on a frame with linear bearings. These devices were locked and embedded in a 7-m walkway and made less apparent by the stationary decoy platforms. Once released, the moveable platforms were free to slide along the track on the linear bearings. (B) The instantaneous gait stability for an instantaneous COM state (diamond, ie, its position and velocity) is the shortest distance (double-headed arrow) between the computational boundary (dark black line) and the COM state. (C) COM state trajectory on the nonperturbed trial from 2 participants who subsequently experienced either a fall (participant A, solid line) or a loss of balance (participant B, dashed line) on the immediately subsequent (slip) trial. The shaded area in (B) and (C) is where the model predicts that a backward loss of balance (BLOB) must occur during a slip. The time course of the COM state trajectory is indicated by the small black arrow. Anterioposterior COM position and velocity are normalized to foot length and √g×h, respectively, where g is acceleration due to gravity, and h is the body height. Note that, as per the model predictions, participant A had a less stable COM state (greater distance to boundary) at right touchdown (an instant immediately prior to slip onset, star) and hence was more likely to experience a fall compared to participant B who experienced a backward loss of balance. Archives of Physical Medicine and Rehabilitation 2011 92, 799-805DOI: (10.1016/j.apmr.2010.12.032) Copyright © 2011 American Congress of Rehabilitation Medicine Terms and Conditions