Impact Of Cardiorespiratory Fitness On The Physiological Stress Responses To A Live-fire Training Evolution

Firefighting can exacerbate cardiovascular disease (CVD) risk and has been shown to elevate α-amylase (AA), secretory immunoglobulin-A (SIgA), and cortisol. Data suggest firefighters may not meet cardiorespiratory fitness (CRF) standards. It is unclear if CRF levels impact the stress response to firefighting. Given the premature mortality risk, there is a critical need to understand the impact of CRF on firefighting stress responses. PURPOSE: This study assessed the impact of CRF on the stress response to an LFTE. METHODS: Forty-four (n = 44) firefighters completed a cardiopulmonary exercise test (CPXT) and an LFTE. V̇O2max was estimated via the Foster equation. The occupational CRF standard of 42 ml/kg/min was used to establish a low-fitness group (LF; n = 22) and a high-fitness group (HF; n = 22). Salivary samples were collected pre (baseline [BL]), immediately post (post), and 30-min post the LFTE and analyzed for AA, SIgA, and cortisol. Data were analyzed via a general linear model (GLM) multivariate and univariate analysis. Data are shown as mean and standard deviations. RESULTS: GLM multivariate analysis revealed an overall time effect (p < 0.001, ηₚ2 = 0.218) with no group (p = 0.534, ηₚ2 = 0.053) or group x time effect (p = 0.623, ηₚ2 = 0.026) for the salivary stress biomarkers. The univariate analysis revealed time effects for AA (p < 0.001, ηₚ2 = 0.248), SIgA (p < 0.001, ηₚ2 = 0.262), and cortisol (p = 0.002, ηₚ2 = 0.140); however, no group x time effects were found for AA (p = 0.486, ηₚ2 = 0.015), SIgA (p = 0.502, ηₚ2 = 0.015), and cortisol (p = 0.978, ηₚ2 = 0.000). Significantly higher AA (BL: 110.4 ± 13.6; post: 217.5 ± 24.0; p = 0.003), SIgA (BL: 188.4 ± 14.5; post: 274.5 ± 23.9; p = 0.003), and cortisol (BL: 0.238 ± 0.022; post: 0.433 ± 0.056; p = 0.003) concentrations were noted immediately post-LFTE than baseline concentrations. Only AA concentrations remained elevated at 30-min post-LFTE compared to baseline (BL: 110.4 ± 13.6; post: 139.6 ± 14.3; p = 0.003). CONCLUSIONS: These data demonstrate the CRF level does not impact the physiological stress response to firefighting. Certainly, it is reasonable to believe that a more fit firefighter will be able to carry out physically demanding occupational tasks; however, future work should elucidate the impact that CRF may have on the stress response to fire-suppressive activities.