Introduction
Firefighting entails acute operational demands layered onto rotating 24-h shifts, with implications for stress biology, sleep, and psychological health. Evidence integrating wearable physiology with psychosocial indicators in real service conditions remains scarce.
Purpose
To characterize short-term (within-shift) changes in physiological stress and sleep alongside dispositional, work condition, and health-related self-reports in a municipal firefighter service, and to describe variability by station and shift.
Method
We analysed data from 145 firefighters (97% men; mean age = 46.9 ± 9.0 years) working 24-h rotating shifts across four stations and five shifts. Measures included: salivary alpha-amylase and cortisol collected pre- and post-shift; Fitbit-derived heart-rate variability (HRV; RMSSD and LF/HF) and deep non-REM sleep; and validated self-reports (e.g., perceived stress, burnout, emotion regulation, resilience, etc.). Operational workload was indexed by types of interventions and frequency.
Results
Across the duty, alpha-amylase decreased while cortisol increased; both biomarkers showed marked variability across stations and shifts. Self-reports indicated low-moderate stress and low burnout, alongside high resilience. Wearable HRV and deep-sleep metrics were feasible to collect and varied by station/shift. During the observation window, 85 interventions were recorded. A predictive model proposes a dual-path mechanism linking emotional demands and station conditions with firefighters' health outcomes. Suboptimal station conditions are posited to increase acute fatigue, undermining recovery between shifts and—through this energetic pathway—contributing to higher burnout and lower well-being. Thus, the model distinguishes a cognitive-affective route (stress → burnout/well-being) from a physiological-energetic route (fatigue → recovery → burnout/well-being).
Conclusions
Station/shift variability suggests organizational and scheduling levers may shape sleep and autonomic recovery. Integrating wearables with multi-level self-reports is feasible and informative for targeted fatigue- and stress-mitigation strategies. Interventions should combine emotion-regulation and supervisory support (to buffer stress) with environmental and scheduling improvements (to reduce fatigue and protect recovery).