Effect of physical training on autonomic nervous system

The purpose of this study was to investigate whether intensity of physical training affects the adaptation of autonomic nervous system, and whether a change of heart rate at rest (HRrest) results from a change of autonomic nervous system activity. Twenty true subjects were randomly assigned to three groups, which were high intensity training group (n = 7, H gruop), low intensity training group (n=8, L group) and control group (n=6, C group). Subjects of H and L group trained for 8 weeks, 3 times/week, 60 minutes, using a cycle ergometer. The target heart rate of the training was set at 150 bpm in H group, or 100 bpm in L group. V̇O₂max and work rate at training were measured before and after training session. R-R intervals and norepinephrine (NE) were measured every 2 weeks. Spectral analysis (FFT method) was applied to the continuous 5 minutes R-R intervals, and areas of 0.05-0.15Hz (Pl) and 0.15 - 1.0Hz (Ph) were caluculated to evaluate sympathetic nervous (Pl/Ph) and vagal (Ph) activities. HRrest was also caluclated from 5 minutes R-R intervals. V̇O₂max and work rate at training significantly increased only in H group. HRrest, Pl/Ph, Ph and NE were not significantly different from pre-training. There were inter-individual correlations (p< 0.05) between the change of HRrest from pre-training and that of Ph from pre-training. However, no significant correlations were shown in relationships between the change of HRrest and the change of both Pl/Ph and NE from pre-training. These results suggest that intensity of physical training does not have any effects on the change of the autonomic nervous system, and that the change of HRrest by training would be mainly due to the change of parasympathetic nervous system activity.