Glenohumeral contact forces and muscle forces evaluated in wheelchair-related activities of daily living in able-bodied subjects versus subjects with paraplegia and tetraplegia.

OBJECTIVE To estimate the differences in glenohumeral contact forces and shoulder muscle forces between able-bodied subjects and subjects with paraplegia and tetraplegia during wheelchair-related activities of daily living (ADLs). DESIGN Kinematics and external forces were measured during wheelchair ADLs (level propulsion, weight-relief lifting, reaching) and processed by using an inverse dynamics 3-dimensional biomechanical model. SETTING Biomechanics laboratory. PARTICIPANTS Five able-bodied subjects, 8 subjects with paraplegia, and 4 subjects with tetraplegia (N = 17). INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Glenohumeral contact forces and shoulder muscle forces. RESULTS Peak contact forces were significantly higher for weight-relief lifting compared with reaching and level propulsion (P < .001). High relative muscle force of the rotator cuff was seen, apparently needed to stabilize the joint. For weight-relief lifting, total relative muscle force was significantly higher for the tetraplegia group than for the able-bodied group (P = .022). CONCLUSIONS Glenohumeral contact forces were significantly higher for weight-relief lifting and highest over the 3 tasks for the tetraplegia group. Without taking paralysis into account, more muscle force was estimated for the subjects with tetraplegia during weight-relief lifting.