The relationship between resting bradycardia with endurance training and autonomic nervous system modulation

We investigated whether the autonomic nervous system (ANS) modulation contribute to the bradycardia induced by endurance training. First, the meta-analysis approach was used to collect group mean values of maximal oxygen consumption (Vo(2)max) and heart rate variability (HRV) from 14 studies involving 30 groups and 485 subjects. Subsequently, we performed a cross-sectional (n=116) and intervention (n=training group : 10 and control group : 6) studies. In both studies, ANS modulation was estimated by spectral analysis of HRV. In the meta-analysis and cross-sectional study, HR and natural logarithmic high frequency power (In HF power) were correlated with Vo(2)max or peak oxygen uptake (peak Vo(2)). The significant negative correlations were found between HR and In HF power ( meta-analysis and the cross-sectional study; r(2) = 0.42 and 0.44, respectively). Endurance training in the intervention study increased peak Vo(2) and resting In HF power, and decreased resting HR. These results strongly suggest that endurance training induces an increase in resting ANS modulation especially parasympathetic modulation. Furthermore, about half of the variability of resting HR can be accounted for by difference in parasympathetic modulation.