Effect of seat height on manual wheelchair foot propulsion, a repeated-measures crossover study: part 1 - wheeling forward on a smooth level surface.

PURPOSE: To test the hypotheses that, during manual wheelchair foot propulsion forward on smooth level surfaces, 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 10 m on a smooth level surface at 5 seat heights in random order, ranging from 5.08 cm below to about 5.08 cm above lower-leg length. 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 0.20 m/s and in push effectiveness of 0.20 m/cycle. The trend for push frequency was also significant (p = 0.003) but the effect size was smaller. Perceived difficulty increased with seat height (p < 0.001). The video-recordings provided qualitative kinematic data regarding the seated "gait cycles". CONCLUSIONS: During manual wheelchair foot propulsion forward on smooth level surfaces, lowering the seat height increases speed and push effectiveness, and decreases perceived difficulty. CLINICAL TRIAL REGISTRATION NUMBER: NCT03330912.Implications for RehabilitationGenerally, wheelchairs used for forward foot propulsion should have a seat height that is 2.54-5.08 cm less than the sitting lower-leg length.Clinicians should, however, take into consideration other functions that may be adversely affected by lowering the seat height.