Low fitness is associated with exercise abnormalities among asymptomatic firefighters

Background: Low cardiorespiratory fitness (CRF) has been repeatedly linked to cardiovascular morbidity and mortality, while higher CRF levels are protective. This relationship is likely to be highly relevant in firefighters, who have increased risk of cardiovascular disease (CVD) mortality during strenuous emergencies, which can require prolonged periods of near-maximal heart rates (HR) and high workloads. Abnormalities during maximal stress testing could mark future CVD risk during strenuous duties. Aims: To determine if low CRF among asymptomatic firefighters is associated with higher risk of electrocardiographic (ECG) and autonomic abnormalities during maximal exercise stress testing and recovery. Methods: Male career firefighters completed a maximal stress test exercising to volitional exhaustion (mean maximal age-predicted HR achieved 98%, standard deviation (SD) = 6.5). CRF was measured as maximal metabolic equivalents (METS) achieved. Abnormal exercise tests included the following: abnormal HR recovery; chronotropic insufficiency; exaggerated blood pressure response; and ECG abnormalities. The relationship of CRF to stress testing abnormalities was analysed using peak METS categories and peak METS as a continuous variable after adjusting for age, body mass index (BMI) and metabolic syndrome (MetSyn). Results: There were 1149 study participants. CRF was inversely associated with the risk of both (ECG) and autonomic exercise testing abnormalities before and after adjustment for age, BMI and MetSyn. Conclusions: Firefighters with lower CRF are significantly more prone to exhibit abnormal stress test parameters, which may indicate higher future risk of cardiovascular events. As such, firefighters with low CRF (≤12 METS) should receive cardiovascular risk reduction, including efforts to improve their CRF.