Exploration of shoulder load during hand-rim wheelchair start-up with and without power-assisted propulsion in experienced wheelchair users

• Start-up is assumed as a straining and frequent element in hand-rim wheelchair use.
• The intensity of shoulder loading decreased during power-assisted start-up.
• Also reduced peak resultant force with less shoulder abduction
• Use of power-assist might reduce the risk of developing shoulder overuse injuries.

BackgroundFrequent start movements occurred during the day, yielding high upper-extremity stress. The high incidence and impact of shoulder injury on daily life wheelchair use made it clinically relevant to investigate whether power-assisted propulsion is beneficial during the start.MethodsEleven hand-rim wheelchair users performed a start-movement in an instrumented wheelchair on a flat surface. Test order was randomly assigned to propulsion with and without power-assist. For each subject, parameters were averaged over 3 repeated starts. For statistical analysis Wilcoxon Signed Rank test was used.FindingsIntensity of mechanical shoulder loading decreased during power-assisted propulsion for anterior (147.0 (44.8) versus 121.9 (27.4) N; effect size (r) = −.75), posterior (4.8 (14.1) versus 2.7 (11.6) N; r = −.64) and inferior directed forces (82.6 (27.9) versus 68.9 (22.6) N; r = −.78) and abduction (20.2 (14.6) versus 12.9 (7.8) Nm; r = −.88) and extension moments (20.3 (10.7) versus 13.7 (9.1 Nm; r = −.88). Peak resultant force at the rim significantly decreased from 133.5 (38.4) N to 112.2 (25.4) N (r = −.64) and was accompanied by significant decreased shoulder abduction (35.3 (6.7) versus 33.3 (6.8); r = −.67) and significant increased shoulder extension (13.6 (16.3) versus 20.3 (19.1); r = −.78) during power-assisted start-up.InterpretationPower-assist hand-rim wheelchairs are effective in reducing external shoulder load and partly effective in reducing force generation in extremes of shoulder motion during start-up. The use of power-assist wheels might reduce the risk of developing shoulder overuse injuries.Clinical trial registration number: NTR2661.