Influence of Body Composition on Post-Exercise Parasympathetic Reactivation of Firefighter Recruits

Firefighters have a sustained risk for experiencing a sudden cardiac event after completing a fire call. Heart rate recovery (HRR) can be utilized to characterize autonomic nervous system (ANS) recovery and has been linked to cardiac events. Research suggests that body composition influences post-exercise HRR responses in non-firefighter populations. The purpose of this study was to examine the influence of body mass index (BMI), waist circumference (WC), and percent body fat (BF) on the HRR response of firefighter recruits. BMI (kg·m^-2), WC (cm), and BF (%) data from 57 firefighter recruits were collected. HRR (b·min^-1) data were collected at completion (HR₀), as well as 15 (HR₁₅), 30 (HR₃₀), 45 (HR₄₅), 60 (HR₆₀), 120 (HR₁₂₀), and 180 (HR₁₈₀) seconds following a submaximal step test, and commonly utilized clinical HRR indices were calculated (ΔHRR₃₀, ΔHRR₆₀, ΔHRR₁₂₀, and ΔHRR₁₈₀). After controlling for sex, linear mixed regression models did not identify significant interactions between body composition (ps > 0.05) and HRR response across time. However, significant (ps < 0.05) indirect semi-partial correlations were identified between BF and ΔHRR₃₀ (r_sp = -0.31) and ΔHRR₆₀ (r_sp = -0.27), respectively. Reducing overall BF (vs. BMI or WC) should be prioritized to improve the post-exercise ANS recovery of firefighter recruits.