title: The Biomechanical Mechanisms of Fall Risk on Stairs with Inconsistent Step Dimensions
Creators: name: Francksen, N
Publisher: name: Liverpool John Moores University
Year: 2020

description: Stair falls frequently happen, affecting people of all ages and impact on a person’s independence. Not only do high rises and shallow goings increase the fall risk but inconsistent dimensions are commonly reported in stair fall investigations. Literature speculates that, the mechanistic reasoning behind these falls occur because individuals do not detect the inconsistency and therefore do not adjust their stepping behaviour. However, these hypotheses are based on observations and assumptions derived from normal stepping behaviour on consistent stairs and have not yet been experimentally tested. Therefore, the purpose of this thesis is to empirically test the mechanisms by which inconsistencies in rise and going dimensions could cause falls in younger and older adults. Twenty-six younger adults (24±3 y, 1.74±0.09 m, 71.41±11.04 kg) and thirty-two older adults (70±4 y, 1.68±0.08 m, 67.90±14.10 kg) ascended and descended an instrumented staircase in three conditions: 1) consistent dimensions (all steps riser =200 mm and going =250 mm), 2) inconsistent rise (third step was raised 10 mm, causing the fourth step to have 10 mm reduced riser) and 3) inconsistent going (third step was made 10 mm shorter, causing second step to have a 10 mm increased going). Data were collected from 3D motion capture and force plates embedded in the bottom four steps. Data were used to quantify and compare stepping mechanics and centre of mass control in the consistent condition to that in the inconsistent rise and inconsistent going conditions. In the inconsistent rise condition (Chapter 3), during ascent clearances of both groups were reduced (≈9 mm, F=48.4, p=.001) over the higher step-edge, increasing trip risk. During descent, percentage foot contact lengths decreased (≈2%, F=9.1, p=.004) on the inconsistently higher step for both groups, possibly increasing the risk of a slip. Foot centre of mass (CoM) trajectories during swing prior to contact, revealed that there were no alterations to stepping behaviour prior to contact with the inconsistently higher rise step, causing a magnitude of change that was comparable to the 10 mm manipulation. In the inconsistent going condition (Chapter 4), during descent percentage foot contact lengths of both groups were not significantly different to the consistent condition (≈1%, F=2.5, p=.121). Foot CoM trajectories during swing confirmed that, individuals changed their stepping behaviour in late swing prior to contact with the shorter step, contradicting previous assumptions. Additionally, younger adults then had reduced clearances over the inconsistently longer step, which could increase their trip risk. During ascent, there were interaction effects detected between stair configurations and age groups. On the shorter step, foot contact lengths were increased for younger adults (≈+2.2%) and decreased for older adults (≈-2.8%) (interaction: F = 8.8, p=.004), this could increase the chances of a miss-step for the older adults. These differences seemed to stem from positioning on the walkway before transition. Younger adults were 8 mm closer to the stairs in their level-ground step, whereas older adults were 14 mm further away in the inconsistent going condition (interaction effect, p=.048). Descending balance parameters were affected by the presence of the inconsistent dimensions (Chapter 5). There were interactions between the CoM accelerations at 23.6%-31.9% and 73.4%-77.0% of stance on Step4 (p=.008 and p=.035, respectively) prior to contact with the inconsistent shorter going step, balance parameters after contact were minimally affected. Whereas for the inconsistent rise condition, balance was altered at contact with the higher step due to more posteriorly directed forces between 16.5%-22.2% of stance on Step3 (p=.020) and higher peak coefficients of friction (p=.003), this could increase the risk of slipping during loading. Despite increased loading rates (p