Effect of seat height on manual wheelchair foot propulsion, a repeated-measures crossover study: part 2 - wheeling backward on a soft surface.

Purpose: The aim of this study was to test the hypotheses that, during manual-wheelchair foot propulsion backward on a soft surface, lowering the seat height increases speed, push frequency and push effectiveness, and decreases perceived difficulty.Materials and methods: In a repeated-measures crossover study, 50 able-bodied participants used one foot to propel a manual wheelchair 5 m backward on a soft surface at 5 seat heights, ranging from 5.08 cm below to about 5.08 cm above lower-leg length, in random order. We recorded Wheelchair Skills Test (WST) capacity scores and used the Wheelchair Propulsion Test (WPT) to calculate speed (m/s), push frequency (cycles/s) and push effectiveness (m/cycle). We also recorded the participants' perceived difficulty (0-4) and video-recorded each trial.Results: WST capacity scores were reduced at the higher seat heights. Using repeated-measures models (adjusted for age, sex and order), there were negative relationships between seat height and speed (p < 0.0001) and push effectiveness (p < 0.0001). Lowering the seat height by 5.08 cm below lower-leg length corresponded to improvements in speed of 0.097 m/s and in push effectiveness of 0.101 m/cycle. The trend for push frequency was also significant (p = 0.035) but the effect size was smaller. Perceived difficulty increased with seat height (p < 0.0001). The video-recordings provided qualitative kinematic data regarding the seated "gait cycles".Conclusions: During manual-wheelchair foot propulsion backward on a soft surface, lowering the seat height increases speed and push effectiveness, and decreases perceived difficulty.IMPLICATIONS FOR REHABILITATIONBackward wheelchair foot propulsion on soft surfaces is affected by seat height.Speed (m/s) is improved if the seat height is lowered.Push effectiveness (m/gait cycle) is improved if the seat height is lowered.Perceived difficulty of propulsion is lower if the seat height is lowered.