RESUMO
In the present experiment, we evaluated the impact of rapid heat stress (RHS) on salivary cortisol and C-reactive protein production pre-RHS, post-RHS, and 24 and 48 h post-RHS exposure among firefighters. Previous research has demonstrated that RHS increases salivary cortisol during RHS and immediately post-RHS exposure. However, no research has evaluated the duration necessary to return to baseline cortisol levels following RHS. Additionally, no studies have analyzed the impact of RHS on inflammatory biomarkers, such as C-reactive protein. This study hypothesized that salivary cortisol and C-reactive protein levels would increase following RHS and then return to pre-RHS levels within 24 h post-exposure. Twenty-four participants performed a steady-state treadmill protocol in an environmental chamber (35 °C; 45% humidity) in full firefighter personal protective equipment until reaching either a core temperature (Tc) of 39 °C or a volitional maximum. The subjects had their saliva collected via the passive drool protocol pre-RHS, post-RHS, and 24 and 48 h post-RHS. Pre-RHS of 0.23 ± 0.03 µg/dL increased post-RHS to 0.51 ± 0.06 µg/dL (p < 0.001). This finding supports previous literature demonstrating the immediate impact of RHS. There were no changes in C-reactive protein. The novel finding of this study is that salivary cortisol levels return to baseline in the 24 h post-RHS exposure. This indicates that 24 h is recommended to recover from RHS and should be applied to prevent the chronic stress response.
