Fig. 4

Impact force as a function of impact position for wheelchair tips. Colors represent increasing contact force. All restrained passenger simulations showed contact forces below 3000 N. Unrestrained passengers showed a broad range of impact forces with most simulations exceeding 7000 N. There was a significant relationship between impact position and increased impact force. In the restrained simulations (blocks) the head position is tightly clustered, whereas the unrestrained occupants (triangles) show greater variation in head impact locations relative to the wheelchair. Positive x value indicates the rider moving forward relative to the chair and positive z values indicate the rider moving upward normal to the seat plane