Firefighters face repeated bouts of physiological arousal and sustained mental and emotional strain, which, if unmanaged, can detrimentally impact their health. Adding to these demands, call volumes have nearly tripled over the past 40 years. Despite evidence demonstrating the impact of call volume on a firefighter’s health, a real-time method for effectively tracking and managing stress levels is lacking. Additionally, call volume is commonly used to gauge workload. However, it remains unclear how variations in call volume affect health outcomes such as autonomic regulation, sleep, body fat, and aerobic fitness. The purpose of this dissertation was to examine the effects of a 24-hour shift on heart rate variability (HRV) in career firefighters and explore how HRV related to call volume, sleep duration, maximal aerobic capacity, and post-traumatic stress disorder (PTSD) symptoms. Differences in sleep duration, body fat percentage, maximal aerobic capacity, and HRV among low, moderate, and high call volume groups were investigated.
