Abstract

Regular aerobic training has been suggested to protect the heart by increasing cardiac vagal activity. The aims of this study were to evaluate the autonomic regulation of heart rate (HR) during and after exercise, during aerobic training interventions and to study the association between autonomic regulation and the training response in healthy male subjects. HR variability assessment was used to study the effects of exercise on autonomic regulation of HR.

The whole study population consisted of 70 volunteer male subjects (age 36 ± 10 years). The recovery of the autonomic nervous system after prolonged exhaustive exercise was studied in a group of 10 subjects. The training interventions included 51 subjects. The effects of training volume on autonomic regulation were assessed (n = 46) during a controlled eight-week training intervention. The association between training and autonomic regulation was studied (n = 24) during a ten-month period of home-based training based on the American College of Sports Medicine recommendations. Finally, the association between autonomic regulation and the individual training response was analysed (n = 51) after eight weeks of controlled training.

The recovery rate of vagally mediated high-frequency (HF) power of HR variability after prolonged exhaustive exercise was associated with physical fitness (r = -0.71, P < 0.016). Moderate (3 hours/week) and high-volume (6 hours/week) aerobic training results in a similar increase in HR variability indices. HF power increased from 6.19 ± 1.02 to 6.76 ± 0.96 ln ms² (P < 0.001) and from 6.61 ± 1.01 to 7.12 ± 0.92 ln ms² (P < 0.001) after moderate and high-volume training, respectively. During the home-based training program, the changes in HF power were associated with the changes in the fitness (r = 0.44, P < 0.05), body mass index (r = -0.44, P < 0.05) and the amount of training (r = 0.41, p < 0.05). Finally, a significant correlation was observed between the training response and the baseline HF power (r = 0.52, P = 0.001). HF power accounted for 27 % of the change as an independent predictor of the aerobic training response.

In conclusion, a highly controlled aerobic training intervention of eight weeks, including six 30-min sessions a week at an intensity of 70–80 % of maximum HR, is a sufficient intervention to increase cardiac vagal outflow and the offered home-based training according the current guidelines maintains the high cardiac vagal outflow. Secondly, high vagal activity at baseline is associated with the improvement in aerobic fitness caused by aerobic training, suggesting that the cardiovascular autonomic function is an important determinant of the response to aerobic training.