Impact of Cardiorespiratory Fitness on Markers of Cardiovascular Disease in Professional Firefighters

Higher cardiorespiratory fitness (CRF) levels (V̇O2max) are associated with lower oxidative stress and inflammatory markers in addition to lower cardiovascular disease (CVD) risk; however, there are a lack of data examining this relationship among firefighters. CVD is the leading cause of mortality among firefighters and correlates with low CRF. PURPOSE: To examine differences in markers of CVD risk between firefighters classified as having either high or low levels of CRF. METHODS: Forty-six professional firefighters performed a maximal graded exercise test (GXT; Bruce Protocol), where V̇O2max was estimated from the Foster equation using time to exhaustion. Fasted blood samples were also taken to assess traditional and non-traditional biomarkers of CVD risk: HDL, LDL, glucose, cholesterol, triglycerides, advanced oxidation protein products (AOPP), homeostatic model assessment for insulin resistance (HOMA-IR) and C-reactive protein (CRP). Body fat percentage (BF%) was determined via Dual-Energy X-Ray Absorptiometry (DEXA),V̇O2max values were categorized based on American College of Sports Medicine (ACSM) guidelines to establish a high fitness group (n=19; V̇O2max = 44.7 ± 5.2 ml·kg-1·min-1; age = 35.94 ± 9.73 yrs; height = 178.86 ± 7.28 cm; waist circumference = 35.5 ± 2.73 cm; BF% = 19.9 ± 2.66) and a low fitness group (n=27; V̇O2max = 28.2 ± 4.9ml·kg-1·min-1; age = 38.5 ± 9.33 yrs; height = 179.21 ± 8.48 cm; waist circumference = 40.06 ± 4.29 cm; BF% = 27.2 ± 5.07). Non-parametric Mann-Whitney U tests were used to assess differences in CVD risk markers between the high and low fitness groups. Effect sizes were calculated as Cohen’s d (i.e., small [0.2-0.5], medium [0.5-0.8], large [\u3e 0.8]). RESULTS: Participants classified as high fitness had significantly (p \u3c 0.05) higher V̇O2max and HDL concentrations coupled with significantly lower BF%, cholesterol, triglycerides, LDL, insulin, HOMA-IR, CRP, and AOPP. Half of the observed differences demonstrated a medium effect size (LDL, insulin, HOMA-IR, CRP, and AOPP), while large effect sizes were noted for V̇O2max, BF%, cholesterol, triglycerides, HDL, LDL/HDL risk ratio. CONCLUSION: The high fitness group exhibited lower CVD risk levels and higher HDL levels compared to the low fitness group. Considering the results, firefighters are encouraged to maintain high CRF as well as lower BF% in an effort to reduce the risk of CVD and on-duty cardiac events