Data from the Centers for Disease Control indicates that over 4-million adult drivers and passengers are treated in US emergency medicine departments annually for whiplash as the result of a motor-vehicle accident. While it is expected that many (> 50%) will recover within the first 2-3 months post injury, some (25%) will never fully recover. Estimated costs for medical and rehabilitative care for the 25% patients with poor functional recovery are ~$100 Billion annually and no treatments have shown to positively influence their outcomes. Unfortunately, in the vast majority of whiplash cases, structural damage on objective imaging is rarely present. Currently, the prevailing opinion is that poor functional recovery is largely influenced by social, psychological and behavioral factors and not biological. While this may be the case in some, our pilot data and previous work has, as a first, demonstrated the rapid and early expression of muscle fatty infiltrates on MRI, signs of disturbed descending control, and muscle weakness in the 25% of individuals with whiplash associated disorders (WAD) with poor functional recovery. The 75% of individuals that recover spontaneously following a whiplash do not manifest such signs and symptoms, suggesting a more severe injury with a biological etiology, in the chronic group. These complex signs and symptoms bear striking similarities to non-WAD patients with incomplete spinal cord injury (iSCI); raising the possibility that chronic WAD is an expression of an initial mild injury to the spinal cord. Both groups present with a paralleled expression of muscle fatty infiltrates, signs of disturbed descending control, psychological distress, and muscle weakness. As such, the goal of this proposal is to test our central hypothesis that chronic WAD is an expression of a mild iSCI. We propose to combine biomechanical, electrophysiological and radiological measures to demonstrate that losses in spinal neural substrate, increased fatty infiltrates in select neck and lower extremity muscles, and the inability to properly activate ankle muscles in patients with chronic WAD is an expression of a mild iSCI. The long-term goals of this research is to improve outcomes in WAD, but before this can be realized, it is crucial we 1) understand the neurophysiological mechanisms underlying poor functional recovery in the 25% of individuals with a seemingly more complex injury and 2) consider and integrate the bio-psycho-social drivers of the clinical course on a patient-by-patient basis. This new knowledge will set the stage for future studies investigating more objective and integrated assessments as well as the development of targeted science-based interventions for a cohort that does not respond well to current intervention strategies.