Wheelchair propulsion is an important part of daily living for many people with spinal cord injuries (SCI's). The aim of this project was to establish the validity of using a new approach for measuring wheelchair propulsion ability. The variation in methods observed by subject's hands in contacting and propelling their wheelchair, namely, using the push rims only; wedging the hands between push rims and tyre and grasping both push rims and tyres, highlighted that earlier studies using instrumented push rims (including the SMART ) for people with tetraplegia would not provide a true indication of propulsion ability for the participants in this study. As a result, a new inertia dynamometer was built and calibrated for measuring wheelchair propulsion ability. Kinetic and kinematic models were developed to calculate wheelchair propulsion parameters such as power output, wheelchair velocity and arm motion patterns. After testing 22 subjects with different SCI levels, the results indicated that arm function was a more important factor in wheelchair propulsion, in terms of power output, than trunk stability and strength. More importantly, people with C5/C6 tetraplegia had a significantly reduced capability in terms of wheelchair propulsion compared with other subjects with a lower lesion (T1-T8, T9-T12 and L1-S5). A further study for quantifying the contribution of triceps function on improving wheelchair propulsion for people with tetraplegia was performed by comparing kinetic and kinematics parameters in C5/C6 tetraplegia subjects. Depending on the control of elbow extension, the subjects were divided into groups with: no active elbow extension, deltoid to triceps transfer surgery (TROIDS) to provide elbow extension, and incomplete C5/C6 tetraplegia with retained active triceps function providing elbow extension. The results demonstrated that the restoration of triceps following TROIDS surgery not only allows active elbow extension, but also increased the amplitude and strength as well as the speed of arm movement. Finally, the results also point to TROIDS allowing a more pronounced and natural push phase and an improved arm movement pattern during both propulsion and recovery phase under normal and extreme conditions.