Identification of Call Volume and Aerobic Capacity as Predictors of 24 h Shift Workload in Career Firefighters

Background: Total 24 h shift call volume (VOLUMETOTAL) is a common metric of firefighter workload but overlooks health, fitness, and call types. This study identified call volume metrics and aerobic fitness as predictors of shift workload in active-duty firefighters. Methods: Participants’ (N = 38) peak aerobic capacity (VO2PEAK) was quantified and heart rate and triaxial acceleration were continuously measured on duty before reporting subjective load. Impulse Load (IMPULSE) quantified external load, while Edwards’ Training Impulse (eTRIMP), Foster’s Session Rating of Perceived Exertion (sRPE), and the National Aeronautics and Space Administration Task Load Index (NASA-TLX) quantified internal load. Shift VOLUMETOTAL and volume of fire suppression and/or auto-extrication calls (VOLUMEFIRE1) were quantified. General linear mixed models evaluated these variables as workload predictors and moderators. Results: VOLUMETOTAL and VOLUMEFIRE1 predicted IMPULSE, VOLUMEFIRE1 and VO2PEAK predicted eTRIMP, and VOLUMEFIRE1 predicted both sRPE and NASA-TLX. Conclusions: These findings establish that total call volume informs external workload experienced across a shift, yet the volume of fire suppression and/or auto-extrication calls is specifically indicative of perceived, overall, and cardiovascular workload. Additionally, cardiovascular workload is exacerbated in individuals with lower aerobic fitness.