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 REHABILITATION Backward 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.