Abstract
IntroductionStair falls can be caused by inconsistent stair dimensions. During ascent, inconsistently taller stair risers lead to reduced foot clearances as the inconsistency goes unnoticed. A stair horizontal-vertical illusion increases perceived riser heights and foot clearance and could offset reduced foot clearances over inconsistently taller risers, though this might impact other stair safety measures.MethodTwelve participants (age: 22 (3) years) ascended a seven-step staircase under three conditions: i) all steps consistent in riser height (consistent), ii) a 1cm increase in step 5 riser height (inconsistent) and iii) a 1cm increase in step 5 riser height, superimposed with a stair horizontal-vertical illusion (illusion). Vertical foot clearance, foot overhang, and margins of stability were assessed over step 4, 5 and 6. Perceived riser height due to the illusion was determined through a computer perception test. A One-Way Repeated Measures ANOVA compared biomechanical variables between conditions. A One Sample t test compared perceived riser height to the true height.ResultsOver the inconsistent step 5, foot clearance reduced by 0.8cm compared to consistent. Illusion increased foot clearance by 1.1cm and decreased foot overhang by 4% compared to inconsistent. On step 4 the illusion led to more anterior instability compared to inconsistent. Illusion and inconsistent led to more mediolateral stability compared to consistent. The illusion increased perceived riser height by 12%.DiscussionFoot clearance reductions over inconsistently taller risers can be offset by a stair horizontal-vertical illusion. Additional benefits included a safer foot overhang and unaffected stability over the inconsistent riser. Changes to step 4 stability might have resulted from leaning forward to look at the step 5 illusion. The stair horizontal-vertical illusion could be a practical solution for inconsistently taller stair risers, where a rebuild is usually the only solution.
Highlights
Stair falls can be caused by inconsistent stair dimensions
On step 4 the illusion led to more anterior instability compared to inconsistent
The inconsistent condition reduced foot clearance by 0.8cm when compared to the consistent (p = .007, g = .689), and the illusion condition increased foot clearance by 1.1cm when compared to the inconsistent condition (p = .002, g = 1.043) (Fig 3A)
Summary
Stair falls can be caused by inconsistent stair dimensions. During ascent, inconsistently taller stair risers lead to reduced foot clearances as the inconsistency goes unnoticed. The stepping action on stairs is typically an intuitive response to the step dimensions apparent to a stair user [9] This response is informed by the visually perceived step size [10,11,12] and can be fine-tuned by somatosensory feedback (i.e. when the foot lands on the stair tread) from the first few repetitions of the stepping action on a specific staircase [11, 13]. This somatosensory information results from foot contact on steps and the positional feedback from the movement of the lower limbs over each step. Over a perceptually taller obstacle for example, Rhea, Rietdyk [11] found foot clearances initially increase in an obstacle crossing task due to the perceived obstacle size, but over repeated trials, foot clearance height reduces likely due to somatosensory feedback
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
