Objective measures of rollator user stability and device loading during different walking scenarios

Abstract

Walking aids are widely used by older adults, however, alarmingly, their use has been linked to increased falls-risk, yet clinicians have no objective way of assessing user stability. This work aims to demonstrate the application of a novel methodology to investigate how the type of walking task, the amount of body weight supported by the device (i.e., device loading), and task performance strategy affect stability of rollator users. In this context, ten users performed six walking tasks with an instrumented rollator. The combined stability margin "SM" was calculated, which considers user and rollator as a combined system. A Friedman Test was used to investigate the effects of task on SM and a least-squares regression model was applied to investigate the relationship between device loading and SM. In addition, the effects of task performance strategy on SM were explored. As a result, it was found that: the minimum SM for straight line walking was higher than for more complex tasks (p<0.05); an increase in device loading was associated with an increase in SM (p<0.05); stepping up a kerb with at least 1 rollator wheel in ground contact at all times resulted in higher SM than lifting all four wheels simultaneously. Hence, we conclude that training should not be limited to straight line walking but should include various everyday tasks. Within person, SM informs on which tasks need practicing, and which strategy facilitates stability, thereby enabling person-specific guidance/training. The relevance of this work lies in an increase in walking aid users, and the costs arising from fall-related injuries.

Fig 1. Examples of combined centre of pressure, combined base of support and system Stability Margin.

Examples of combined centre of pressure, combined base of support and system Stability Margin for 3 cases: A) all 6 feet on the ground; B) 4 rollator feet on the ground and user in single support on their right foot; C) user in double support and rollator fully airborne (e.g. being lifted up a step). Grey foot prints indicate feet that are grounded; white foot prints indicate feet that are airborne.

Fig 2. Instrumented rollator system.

Details of: A) load cell; B) rear leg design; C) front leg design; D) pressure-sensing insole system; E) infrared camera.

Fig 3. Example data sets for two rollator users (P1: Fit, P8: Frail) walking in a straight line.

Top: movement pattern showing times when wheels and feet are in contact with the ground. Middle: stability margin ‘SM’. Bottom: device loading ‘DL’.

Fig 4. Box plot of the minimum SM for each task across the 10 participants.

The bottom and top edge of the boxes indicate the first and third quartile, the thicker line inside the box represents the median, and the whiskers below and above the box show the minimum and maximum values respectively. Circles denote outliers as identified automatically by the software R. “Straight”: straight line walking, “Back”: Backwards walking, “Obstacle”: obstacle crossing, and “Step”: stepping up a kerb.

Fig 5

Mean (weighted) values of β for A) the 10 participants and B) the 6 tasks.