Influence of Cardiorespiratory Fitness on Cardiac Autonomic Recovery Among Active-Duty Firefighters

Abstract Cornell, DJ, Flees, RJ, Shemelya, CM, and Ebersole, KT. Influence of cardiorespiratory fitness on cardiac autonomic recovery among active-duty firefighters. J Strength Cond Res 38(1): 66–73, 2024—It has been suggested that an inability of the autonomic nervous system (ANS) to recover after strenuous events is a potential cause of sudden cardiac death among firefighters. The purpose of this study was to examine the influence of cardiorespiratory fitness (CRF) on the heart rate recovery (HRR) kinetics of firefighters. Thirty-seven male career active-duty firefighters completed both a submaximal step test and a maximal treadmill graded exercise test. A monoexponential curve was fit to postexercise submaximal and maximal HRR data of each subject. Subjects were placed into Low CRF ( n = 13) and High CRF ( n = 24) groups based on the standard peak aerobic capacity (V̇O 2 peak) criterion of <42 ml·kg −1 ·minute −1 and ≥42 ml·kg −1 ·minute −1 , respectively. After controlling for age and body mass index, CRF was significantly ( p < 0.05) correlated with the decay rate ( ) and asymptote ( ) after submaximal exercise ( r sp = −0.556; r sp = −0.637, respectively), as well as the , , and amplitude ( ) after maximal exercise ( r sp = −0.353; r sp = −0.416; r sp = 0.603, respectively). High CRF firefighters demonstrated a significantly faster after both submaximal ( p = 0.003) and maximal exercise ( p = 0.043), a lower after submaximal exercise ( p = 0.002), and a higher after maximal exercise ( p = 0.001), than Low CRF firefighters. Greater CRF was associated with enhanced HRR kinetics after submaximal and maximal exertion, suggesting that CRF may positively influence the ANS recovery of firefighters.