Longitudinal relationship between onset of physical symptoms and functional impairment.

Patients with chronic physical symptoms (e.g., chronic pain) often have significant functional impairment (i.e., disability). The fear avoidance model is the dominant theoretical model of how the relationship between chronic physical symptoms and functional impairment develops and proposes a cyclical/bidirectional relationship. There has never been a definitive test of the proposed bi-directional relationship. The current study followed 767 Operation Enduring Freedom/Operation Iraqi Freedom soldiers from pre-deployment, when they were relatively healthy, to 1 year after deployment, when it was anticipated that symptoms would increase or develop. Over the four assessment time points, physical symptom severity consistently predicted worse functional impairment at the subsequent time point. Functional impairment did not show a consistent relationship with worsening of physical symptom severity. These findings suggest that changes to functional impairment do not have a short-term impact on physical symptom severity.