Title: Manipulating the appearance of stairs to improve safety
Funder: Department of Health (England)

Abstract: Research Design: A repeated measures laboratory based study investigating adaptive gait in independently mobile older people.Setting. The gait and vision laboratory at the University of Bradford.Target population: Subjects will be recruited from a group of 50 retired volunteers who regularly sit as patients in undergraduate clinics at the University’s Eye Clinic and from a group of 200 older people on the mailing list of Bradford Older People’s Forum. Healthy subjects will be recruited using exclusion and inclusion criteria used previously.Intervention being evaluated: Adaptive gait when ascending and descending steps and stairs will be assessed with and without a variety of modifications to the appearance of both single and multiple steps.Measurement of outcomes: In all stepping experiments three-dimensional lower limb segmental kinematic data of the stepping action will be collected (at 100Hz) using an eight-camera motion capture system (Vicon MX; Oxford Metrics Ltd Oxford UK) with ground reaction forces collected as subjects step from a force platform onto or from a step that is placed directly over an adjacent force platform (OR6-7; AMTI Boston MA). We have used this approach successfully in many previous experiments and many other leading gait labs use it. Our own work and that of others has identified gait and stepping parameters that are important for safe stepping in ascent and descent. Parameters analysed will include foot placement before the initial step and foot position on subsequent step treads any hits or scuffs of the step maximum foot/toe elevation vertical and horizontal heel (descent) or toe (ascent) clearance gait velocity and dynamic stability.In addition knee-drop and peak landing force will also be determined for step descent. Analysis will also include intra subject variability of these parameters as increased variability in toe clearance for example can lead to a greater likelihood of the step being hit and a trip occurring.Sample size: One primary outcome measure will be the increase in vertical toe clearance with the H-V illusion compared to without it. Using data from the pilot study and assuming a 50% increase in variance for older subjects compared to younger ones; assuming a minimum effect of importance of 5% an estimated standard deviation of 7% and using a two-sided alpha of 0.05 for a paired t-test a sample size of 21 would result in a power of 90%. A sample size of 16 would provide 80% power. This sample size is similar to that used in several recent studies investigating gait adaptations in older subjects (N=19) and suggests that the sample size is appropriate and recruitable. Although the main analysis will incorporate a repeated measuresdesign the effective power is likely to be similar to that using a simple t-test but will depend upon unknown parameters that are difficult to estimate prospectively.Planned analyses: The analysis of step/stair ascent will primarily focus on foot placement relative to the step riser toe clearance over the step edge and foot placement on the upper step or raised surface. The analysis of step descent will primarily focus on heel clearance over the edge or nosing heel placement distance on the lower step’s tread pre-landing kinematics for the descent phase and the mechanics of landing for the initial contact period. Existing ‘in-house’ analysis software that uses previously developed (and reported) biomechanical modelling approaches will be employed to investigate how gait parameters toe and heel clearance and landing behaviour are adapted under the visual illusion. In addition we need to determine whether a mismatch between step height as perceived visually (5-20% higher than actual size) and that perceived via the somatosensory system once the lead-foot has landed on the top of the step could unsettle postural stability particularly for the larger increases in visually perceived step height. If this occurred it could negate any improved safety gains from the increased toe clearance of the step edge. For this reason we intend to also determine the effects of the different illusions on dynamic postural stability by determining the anterior-posterior (A/P) and medio-lateral (M/L) distance between the lateral malleolus of the leading foot and the centre of mass (COM) and the A/P and M/L COM velocity at the instant of foot contact. It is likely that toe and heel clearance will reduce as subjects ascend and descend the stairs and we need to determine whether this learning effect is changed in any way due to the visual illusion by assessing the effect of trial repetition. Data will be analysed using a random effects population averaged model using the Stata version 9.2 statistical programme (Stat Corp. College Station USA). This multivariate model will be obtained using the Generalised Least Squares (GLS) random effects estimator which produces a matrix-weighted average of between-subjects and within-subjects results. An exchangeable correlation structure was judged to be appropriate given the experimental design and due to the exploratory nature of the study no ‘type I’ error adjustment of the alpha level is deemed necessary. Thus level of significance will be set at p<0.05. Factors of interest will be incorporated sequentially and their statistical significance tested using a likelihood ratio test. Factors with a p-value less than 0.10 will be provisionally retained whereas those above 0.10 will be dropped. The final model adopted will be the most parsimonious one felt to adequately explain the data.Project timetables: A workplan documenting the project timetable and including significant milestones is attached to the application (workplan.pdf).


Research activity codes: 3.2 INTERVENTIONS TO ALTER PHYSICAL AND BIOLOGICAL ENVIRONMENTAL RISKS
Health categories: INJURIES AND ACCIDENTS