Purpose: To understand the association between heart rate variability and indices of fatigue, total sleep time, and reaction time in shift workers.

Methods:Ten participants from the British Columbia Wildfire Service management team were examined over a 14-day active fire-line period. Daily measures of subjective fatigue, sleepiness, and alertness were recorded using a visual analog scale. Daily total sleep time was recorded using a wrist actigraph. Cardiac autonomic modulation was examined each morning using heart rate variability (HRV). Three measures of reaction time (simple reaction time, choice reaction tie, and discriminatory reaction time) was examined on days 1, 5, 10, and 14. Multiple linear regression analysis was utilized to examine the association between HRV and indices of fatigue, total sleep time, and reaction time.

Results: Mean shift duration was 13.8 ± 0.77 h. Significant inverse associations were observed between HRV and sleepiness [r = − 0.60, p = 0.000] and fatigue [r = − 0.55, p = 0.000], and a positive association with total sleep time (min) [r = 0.28, p = 0.009]. There were no significant relationships between HRV and simple reaction time (ms) [r = − 0.32, p = 0.182], choice reaction time (ms) [r = − 0.10, p = 0.850], or discriminatory reaction time (ms) [r = − 0.09, p = 0.881].

Conclusions: HRV displayed significant associations with indices of fatigue and sleep, whereby demonstrating its utility as a practical tool for monitoring the development of fatigue in wildland firefighters and for providing insight when to make lifestyle modifications to preserve alertness.