The impact of sleep restriction while performing simulated physical firefighting work on cortisol and heart rate responses
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Physical work and sleep restriction are two stressors faced by firefighters, yet the combined impact these demands have on firefighters’ acute stress responses is poorly understood. The purpose of the present study was to assess the effect firefighting work and sleep restriction have on firefighters’ acute cortisol and heart rate (HR) responses during a simulated 3-day and 2-night fire-ground deployment.
Firefighters completed multiple days of simulated physical work separated by either an 8-h (control condition; n = 18) or 4-h sleep opportunity (sleep restriction condition; n = 17). Salivary cortisol was sampled every 2 h, and HR was measured continuously each day.
On day 2 and day 3 of the deployment, the sleep restriction condition exhibited a significantly higher daily area under the curve cortisol level and an elevated cortisol profile in the afternoon and evening when compared with the control condition. Firefighters’ HR decreased across the simulation, but there were no significant differences found between conditions.
Findings highlight the protective role an 8-h sleep opportunity between shifts of firefighting work has on preserving normal cortisol levels when compared to a 4-h sleep opportunity which resulted in elevated afternoon and evening cortisol. Given the adverse health outcomes associated with chronically high cortisol, especially later in the day, future research should examine how prolonged exposure to firefighting work (including restricted sleep) affects firefighters’ cortisol levels long term. Furthermore, monitoring cortisol levels post-deployment will determine the minimum recovery time firefighters need to safely return to the fire-ground.
KeywordsFirefighters Stress Sleep restriction Physical work Cortisol Heart rate
The authors would like to acknowledge the Bushfire Co-operative Research Centre for providing the financial support for this project. We would also like to thank the firefighters that volunteered their time to participate in this study.
Compliance with ethical standards
Conflict of interest
The authors have no conflicts of interest to declare.
The procedures performed in this study that involved human participants were in accordance with the ethical standards of the institution and the 1964 Helsinki Declaration and its later amendments.
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