The purpose of this study was to assess the adaptive effects of endurance training on autonomic function in athletes with spectral analysis of cardiovascular variability signals. Continuous ECG, arterial blood pressure (ABP), and respiratory signals were recorded from 15 athletes (VO2max > 55 mL.min-1.kg-1) and 15 nonathletes (VO2max < 45 mL.min-1.kg-1) during 10 min at sitting position. Autonomic function was assessed by low frequency power (LF power: 0.06-0.14 Hz) and high frequency power (HF power: the region of the respiratory frequency based on respiratory spectrum) obtained from the autospectra of RR interval, systolic arterial pressure (SAP), and diastolic arterial pressure (DAP) variability signals. The spontaneous baroreflex sensitivity was evaluated by the moduli, BRSLF and BRSHF, of the transfer function between RR interval and SAP variability in LF and HF bands. The resting HR in athletes was significantly lower than that in nonathletes. The HF power, an index of parasympathetic activity, in RR interval spectra were significantly higher in athletes than in nonathletes. Meanwhile, the LF power (an indicator of sympathetic activities contributing to RR interval and of ABP variabilities) showed no significant difference between both groups, although that of athletes was slightly less than that of nonathletes. Also, BRSLF and BRSHF were not significantly different between athletes and nonathletes. These results indicate that endurance training results in the enhanced vagal activities in athletes, which may contribute in part to the resting bradycardia.
The purpose of this study was to assess the adaptive effects of endurance training on autonomic functions in athletes with spectral analysis of cardiovascular variability signals. Continuous ECG, arterial blood pressure (ABP), and respiratory signals were recorded from 15 athletes (VO2max > 55 ml/(kg.min)) and 15 nonathletes (VO2max < 45 ml/(kg.min)) in the sitting position during controlled respiration (tidal volume 700 ml and 15 cycles/min). The autonomic functions were assessed by the normalized low-frequency power (LF power: 0.06-0.14 Hz) and high-frequency power (HF power: the region of the respiratory frequency based on respiratory spectrum) obtained from the autospectra of the RR interval, systolic arterial pressure (SAP), and diastolic arterial pressure (DAP) variability signals. The spontaneous baroreflex sensitivity (BRS) was evaluated by the moduli, BRSLF and BRSHF, of the transfer function between the RR interval and SAP variability in LF and HF bands. The resting HR in athletes was significantly lower than that in nonathletes. In the case of RR interval spectra, the HF power was significantly higher in athletes than in nonathletes, whereas the LF power was significantly lower in athletes than in nonahtletes. These differences might reflect an alteration of sympathovagal interaction with a predominance of parasympathetic activity. However, there was no significant difference in the LF power of SAP and DAP autospectra, reflecting the sympathetic vascular control. The BRSLF and BRSHF were significantly higher in athletes as compared with nonathletes. These results indicate that endurance training induces autonomic imbalance (i.e., the enhanced vagal activities/the attenuated sympathetic tone), which may in part contribute to the resting bradycardia and an increase in the spontaneous BRS in athletes.
Summary:In this study, the effects of long-term physical training on autonomic function in athletes and the response of the autonomic nervous system to dynamic exercise were investigated in nonathletes and athletes with power spectral analysis of heart rate variability (HRV). This study was performed on 13 healthy subjects (5 athletes and 8 nonathletes). Electrocardiographic (ECG) signals were continuously recorded during (1) 15 min of rest in a sitting position on a bicycle ergometer. (2) the dynamic exercise test to the point ofexhaustion, and (3) a 15 min postexercise period. After the recorded ECG signals were sampled at 500 samples/s, the instantaneous HRV signal was constructed from the detected R peaks and then resampled at 4 Hz in order to obtain an evenly spaced time series applicable to power spectral analysis. After linear trends were removed by the robust locally weighted regressioil algorithm, the power spectrum of HRV was estimated for contiguous records of5 12 samples by Burg's maximum entropy method. HRV was quantified by determining the spectral area (power) in two frequency bands, low-frequency power (LF power: 0.054.15 Hz) and high-frequency power (W power: 0.15-0.8 Hz), and their ratio. The comparison between alhletes and nonathletes was performed in terms of the above-mentioned parameters. Although both groups showed similar trends in heart rate (HR) at all stages of protocols, HR in athletes was significantly lower than that in nonathletes during rest and postexercise. In athletes and nonathletes, LF and HF powers gradually decreased with exercise. As recovery progressed, they continued to increase gradually, but remained below resting level. During rest and postexercise, HF power in athletes was significantly (p < 0.05) higher than that in nonathletes. Also, the recovery of HR and HF power during early recovery (PO 1 ) was more rapid in athletes than in nonathletes. Both groups showed an attenuation of LF and HF powers during dynamic exercise. It is likely that, in athletes, the lower HR during rest and the more rapid recovery of HR postexercise was due to a high level of HF power, indicating that vagal activity was enhanced by the adaptive changes in neural regulation produced by long-term physical training.
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