Subjective And Objective Cognitive Fatigue In Wildland Firefighting

Abstract

Wildland firefighting requires continuous attention while exposed to long working hours and sub-optimal sleep. These stressors may induce cognitive fatigue, which poses a risk to worker safety due to reduced awareness. PURPOSE: This pilot investigation examined the effect of sleep and shift characteristics on variables related to cognitive fatigue. METHODS: A within-subject, observational study was conducted on 4 wildland firefighters (3 M, 1F) between July and August of the 2021 fire season. Cognitive fatigue was measured before and after shift, both subjectively, via 7-point scales (Samn-Perelli Fatigue Scale (SPS); Stanford Sleepiness Scale (SSS)), and objectively, via mean reaction time (RT) on the 3-minute psychomotor vigilance task. Sleep variables were measured subjectively via sleep log and objectively via wrist-worn actigraphy. Linear regression analyses were performed to test if shift or sleep variables predicted cognitive fatigue variables. RESULTS: All sleep and shift variables significantly predicted subjective fatigue and sleepiness. SPS was most significantly predicted by shift duration (R2 = .52, F(1, 49) = 52.75, p < .001) and subjective sleep quality (R2 = .24, F(1, 105) = 32.59, p < .001). SSS was most significantly predicted by subjective sleep quality (R2 = .32, F(1, 105) = 49.7, p < .001) and start time (R2 = .21, F(1, 87) = 23.75, p < .001). Mean RT was not significantly predicted by any sleep or shift variable. However, RT was significantly predicted by both subjective sleepiness (R2 = .34, F(1, 55) = 28.52, p < .001) and fatigue (R2 = .12, F(1, 55) = 7.73, p < .01). Mean RT was also non-significantly predicted by objective sleep quality (R2 = .10 F(1, 25) = 2.83, p = 0.105). CONCLUSIONS: Subjective cognitive fatigue measures were significantly predicted by sleep and shift characteristics. Neither sleep nor shift variables significantly predicted mean RT directly, however, RT was significantly predicted by subjective fatigue and sleepiness.