Comparison of shoulder load during power-assisted and purely hand-rim wheelchair propulsion

BackgroundRepetitive forces and moments are among the work requirements of hand-rim wheelchair propulsion that are related to shoulder injuries. No previous research has been published about the influence of power-assisted wheelchair propulsion on these work requirements. The purpose of our study was therefore to determine the influence of power-assisted propulsion on shoulder biomechanics and muscle activation patterns. We also explored the theoretical framework for the effectiveness of power-assisted propulsion in preventing shoulder injuries by decreasing the work requirements of hand-rim wheelchair propulsion.MethodsNine non-wheelchair users propelled a hand-rim wheelchair on a treadmill at 0.9 m/s. Shoulder biomechanics, and muscle activation patterns, were compared between propulsion with and without power-assist.FindingsPropulsion frequency did not differ significantly between the two conditions (Wilcoxon Signed Rank test/significance level/effect size:4/.314/−.34). During power-assisted propulsion we found significantly decreased maximum shoulder flexion and internal rotation angles (1/.015/−.81 and0/.008/−.89) and decreased peak force on the rim (0/.008/−.89). This resulted in decreased shoulder flexion, adduction and internal rotation moments (2/.021/−.77; 0/.008/−.89 and1/.011/−.85) and decreased forces at the shoulder in the posterior, superior and lateral directions (2/.021/−.77; 2/.008/−.89 and2/.024/−.75). Muscle activation in the pectoralis major, posterior deltoid and triceps brachii was also decreased (2/.038/−.69; 1/.015/−.81 and 1/.021/−.77).InterpretationPower-assist influenced the work requirements of hand-rim wheelchair propulsion by healthy subjects. It was primarily the kinetics at rim and shoulder which were influenced by power-assisted propulsion. Additional research with actual hand-rim wheelchair users is required before extrapolation to routine clinical practice.