Trait-like proteomic signatures of stress resilience: correlates of freeze-like response resistance

The freeze-like response is a fundamental defensive mechanism that remains poorly understood despite its potential to impair functioning under acute threat. We examined its biological correlates using untargeted serum proteomics in participants exposed to ecologically valid simulated armed attacks, comparing untrained individuals (n = 20) with experienced police rapid response personnel (n = 20). Freeze-like responses, characterized by unresponsiveness to attack, were assessed via expert video analysis of participant performance during the scenarios. Serum samples collected before and after threat exposure were analyzed via LC‒MS/MS, identifying 1,238 protein groups. Experienced personnel demonstrated markedly greater resistance to freeze-like responses. No significant proteomic changes were observed from pre- to post-exposure in either group, suggesting that freeze-resistance may be associated with stable, trait-like signatures rather than acute stress-responsive processes. Weighted gene co-expression network analysis identified a module strongly correlated with freeze-resistance (r = 0.75, p = 4 × 10−9) and training status (r = 0.71, p = 6 × 10−8), which also correlated with skeletal muscle mass (r = 0.57, p = 8 × 10−5). This module was enriched for processes including extracellular matrix organization, muscle development, carbohydrate metabolism, and antioxidant activity. These molecular patterns may reflect the downstream effects of comprehensive training that integrates physical conditioning, operational experience, and psychological preparation. This study provides the first proteomic characterization of freeze-like response resistance under realistic threat conditions, supporting the view that resilience involves stable physiological adaptations rather than solely reactive stress mechanisms.