The purpose of this research study is to create a subject-specific computer model of wheelchair propulsion to provide information on wheelchair set-up (in particular, axle placement). The primary objective of this study is to investigate the effect of wheelchair set-up on shoulder joint forces during wheelchair propulsion; the secondary objective is to develop a predictive model to identify differences in shoulder joint forces that result from altering the axle position and seating set-up in user's wheelchairs.