The impact of sleep restriction while performing simulated physical firefighting work on cortisol and heart rate responses.
OBJECTIVE
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Centre for Physical Activity and Nutrition Research (C-PAN), Deakin University, 221 Burwood Hwy, Burwood, VIC, 3125, Australia. awolkow@deakin.edu.au.|Bushfire Co-Operative Research Centre, East Melbourne, 3002, Australia. awolkow@deakin.edu.au.
Alexander
A
Wolkow
Centre for Physical Activity and Nutrition Research (C-PAN), Deakin University, 221 Burwood Hwy, Burwood, VIC, 3125, Australia.|Bushfire Co-Operative Research Centre, East Melbourne, 3002, Australia.
Brad
B
Aisbett
Biostatistics Unit, Faculty of Health, Deakin University, Burwood, 3125, Australia.
John
J
Reynolds
Bushfire Co-Operative Research Centre, East Melbourne, 3002, Australia.|Appleton Institute, CQUniversity, Wayville, 5034, Australia.
Sally A
SA
Ferguson
Centre for Physical Activity and Nutrition Research (C-PAN), Deakin University, 221 Burwood Hwy, Burwood, VIC, 3125, Australia.
Luana C
LC
Main
D000222:Adaptation, Physiological; D000328:Adult; D016022:Case-Control Studies; D005260:Female; D061388:Firefighters; D006339:Heart Rate; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D009784:Occupational Diseases / Q000209:etiology / Q000503:physiopathology*; D005082:Physical Exertion / Q000502:physiology; D012463:Saliva / Q000378:metabolism; D012890:Sleep; D012892:Sleep Deprivation / Q000209:etiology / Q000503:physiopathology*; D014940:Work Schedule Tolerance / Q000502:physiology
D006854:Hydrocortisone
Cortisol; Firefighters; Heart rate; Physical work; Sleep restriction; Stress