Abstract
BACKGROUND: Impact forces experienced by the upper limb at the beginning of each wheelchair propulsion (WCP) cycle are among the highest forces experienced by wheelchair users. OBJECTIVE: To determine whether the magnitude of hand/forearm velocity prior to impact and effectiveness of rim impact force are dependent on the type of hand trajectory pattern chosen by the user during WCP. Avoiding patterns that inherently cause higher impact force and have lower effectiveness can be another step towards preserving upper limb function in wheelchair users. METHODS: Kinematic (50 Hz) and kinetic (2500 Hz) data were collected on 34 wheelchair users (16 with paraplegia and 18 with tetraplegia); all participants had motor complete spinal cord injuries ASIA A or B. The four-hand trajectory patterns were analyzed based on velocity prior to contact, peak impact force and the effectiveness of force at impact. RESULTS: A high correlation was found between the impact force and the relative velocity of the hand with respect to the wheel (P<0.05). The wheelchair users with paraplegia were found to have higher effectiveness of force at impact as compared to the users with tetraplegia (P<0.05). No significant differences in the impact force magnitudes were found between the four observed hand trajectory patterns. CONCLUSION: The overall force effectiveness tended to be associated with the injury level of the user and was found to be independent of the hand trajectory patterns.