Influence of Sleep and Exercise Habits on Cardiovascular Strain in Firefighters During Non- Fire Emergency Services

Poor cardiovascular health likely contributes to the high prevalence of cardiac fatalities in firefighters. Inadequate sleep duration and poor sleep quality can contribute to reduced cardiovascular (CV) function and increased CV strain, while aerobic exercise can improve CV function. PURPOSE: To explore whether sleep and exercise habits impact the CV strain experienced by firefighters during non-fire suppression work. METHODS: Data were collected during non-fire suppression shifts, providing emergency services during NCAA DI football games. Questionnaires were completed prior to each shift to gather information about recent sleep and exercise habits. Each firefighter was outfitted with a GPS-enabled physiological monitoring system to measure CV strain throughout the shift. Firefighters were assigned to either bike (BIKE) or logistics (LOG) team. Bivariate correlations were used to explore the strength of relationships between variables; t-tests were used to compare BIKE and LOG results. RESULTS: Firefighters (N = 15; 100% male; mean ± SD, age = 40 ± 11 y; BMI = 33.1 ± 6.2 kg·m-2) worked 8 ± 1 h during 5 games providing non-fire related emergency services. Most firefighters reported “good” quality sleep, for a median duration of 6-7 h per night; similar duration and quality were observed between groups (both P > 0.05). BIKE experienced higher CV strain (54% ± 6% maximal heart rate [HR]) than those assigned to LOG (46% ± 5% maximal HR; P = 0.002). Physiological intensity—a HR-derived measure of cardiac work—was lower for LOG (1.1 ± 0.3 units, out of 10) than BIKE (1.9 ± 0.6 units; P < 0.001). For firefighters assigned to BIKE, higher peak HR was associated with reduced sleep duration (r = -0.67, P = 0.03) and worse sleep quality (r = -0.66, P = 0.04); shorter sleep duration was also associated with higher physiological intensities (r = -0.814, P = 0.004). No association between sleep and CV strain was observed for LOG. Pre-shift (≤48 h) aerobic exercise participation (50% BIKE; 40% LOG) was not associated with magnitudes of CV strain in either group (all P > 0.05). CONCLUSION: In firefighters during non-fire suppression work, pre-shift aerobic exercise does not attenuate CV strain; further investigation is needed to determine if there is a causal relationship between impaired sleep and increased CV strain in firefighters.