Shoulder biomechanics during the push phase of wheelchair propulsion: A multisite study of persons with paraplegia

Objectives: To present a descriptive analysis and comparison of shoulder kinetics and kinematics during wheelchair propulsion at multiple speeds (self-selected and steady-state target speeds) for a large group of manual wheelchair users with paraplegia while also investigating the effect of pain and subject demographics on propulsion. Design: Case series. Setting: Three biomechanics laboratories at research institutions. Participants: Volunteer sample of 61 persons with paraplegia who use a manual wheelchair for mobility. Intervention: Subjects propelled their own wheelchairs on a dynamometer at 3 speeds (self-selected, 0.9m/s, 1.8m/s) while kinetic and kinematic data were recorded. Main Outcome Measures: Differences in demographics between sites, correlations between subject characteristics, comparison of demographics and biomechanics between persons with and without pain, linear regression using subject characteristics to predict shoulder biomechanics, comparison of biomechanics between speed conditions. Results: Significant increases in shoulder joint loading with increased propulsion velocity were observed. Resultant force increased from 54.4 +/- 13.5N during the 0.9m/s trial to 75.7 +/- 20.7N at 1.8m/s (P<.001). Body weight was the primary demographic variable that affected shoulder forces, whereas pain did not affect biomechanics. Peak shoulder joint loading occurs when the arm is extended and internally rotated, which may leave the shoulder at risk for injury. Conclusions: Body-weight maintenance, as well as other interventions designed to reduce the force required to propel a wheelchair, should be implemented to reduce the prevalence of shoulder pain and injury among manual wheelchair users.