Whiplash injuries remain the most common consequence of motor vehicle accidents and account for a significant annual cost to society. In United States alone, whiplash injuries occur in more than one million people every year. It has been reported that the annual cost for whiplash injuries in the USA is $2.7 billion and£ 2.5 billion in the UK. Whiplash injury can reduce victim's quality of life for a significant amount of time, ranging from weeks to few months and sometimes, symptoms may persist for years. Whiplash is a soft tissue injury and the spectrum of injury may include damage to intervertebral ligaments, discs, facet joints and surrounding soft tissues. Whiplash is the most common injury sustained in the rear-end motor vehicle collisions accounting for more than one-thirds to half of the total reported whiplash cases. As an automobile occupant is hit from behind, the forces from the seat back compress the kyphosis of the thoracic spine, which provides an axial load on spine together with shear force which makes it easier for soft tissue injuries to occur. An out of occupant seating posture can change this complex loading compared to the normal posture. Based on the clinical and epidemiological evidence, the axial rotation of the head or inclined head and the body forward postures prior to impact had an increasing whiplash injury risk following automotive rear impacts. There is very less understanding of the injury patterns when the vehicle occupant seating posture is out of position (non-typical posture) and is subjected to a rear end collision. A detailed 3D osseoligamentous human head-pelvis FE model has been developed. The model consists of a skull, vertebrae, viscoelastic discs, frictionless facet joints, nonlinear ligaments, ribcage and pelvis. All of the material properties were derived from literature. The bony structures were modeled as linear elastic material models and the discs and ligaments were modeled as non-linear models. The main aim of this thesis was to develop a head-pelvis FE model to study the influence of different out of occupant seated postures on the injury pattern due to rear end impact loading. The initial goal was to validate the model under static and dynamic loading conditions. Static validation was done in flexion/extension, lateral bending, and axial rotation by comparing the results with cadaveric experimental data. Dynamic validation was performed by providing an input sled acceleration to the FE model and comparing the global as well as intervertebral motion responses with the experimental corridors. FE model was first tested in the normal seating posture in the standard seat with headrest due to the rear end impact of 4g. The headrest and the seat were modeled as a hyperfoam material model in ABAQUS. The normal seating posture was then modified to create different out of occupant seating postures: body forward (BF-body leaned forward by certain angle measured in degrees with respect to the vertical); head turned (HT-head rotated to the right by certain angle measured in degrees), combination of the body forward and head turned posture (BF-HT) and head flexed (HF-head flexed by 20 degrees) that were derived from the literature. The first part of the experiment was to study the effect of progressively increasing body forward seating postures (BF-15, BF-20 & BF-25) on the injury pattern due to the same rear end impact. The next test was to investigate the effect of progressively increasing head turned (HT) seating postures (HT-15, HT-30 & HT-45) on the whiplash injury outcome. Furthermore, head turned, body forward, head flexed and BF-HT postures were compared with the normal seating posture to identify high …