Effects of endurance training on autonomic function in highly fit men: spectral analysis of cardiovascular variability signals

By auto- and cross-spectral analysis of RR interval and arterial blood pressure (ABP) variabilities, effects of endurance training on autonomic function were investigated in 15 highly-fit (FG:Vo/sub 2max/>55 ml/min/spl middot/kg) and 15 unfit (UG:Vo/sub 2max/<45 ml/min/spl middot/kg) men under the condition of controlled respiration (15 breaths/min and 700 ml V/sub T/). The resting HR in FG was significantly (p<0.001) lower than that in UG. The high-frequency (HF) power (an index of cardiac vagal tone) in RR interval spectra was significantly (p<0.001) higher in FG than in UG. The low-frequency (LF) power (an indicator of cardiac sympathetic activities) of RR interval spectra in FG was significantly (p<0.05) lower as compared to UG. The spontaneous baroreflex sensitivity (BRS), as assessed by the moduli of the transfer function between RR interval and systolic blood pressure variabilities, was significantly (p<0.05) higher in FG. These results indicate that endurance training induces a predominant parasympathetic activities in autonomic balance, which may contribute in part to the resting bradycardia and an enhancement in the spontaneous BRS in FG.