The relationship between autonomic nervous activity and physical activity in children

Background: There have been few studies that have reported on heart rate variability and the development of autonomic nervous function in children. This study investigated the relationship between heart rate variabilities at night and physical activity in children. Methods: The study subjects were 29 children, including 17 boys and 12 girls. The daily activity product and heart rate variabilities during sleep at night (00.00-05.00 hours) were measured and several aspects of these parameters were analyzed. In one child (an 8-year-old girl), heart rate variability and the physical activity product were measured for 12 days. Results: There was a negative correlation between the mean R-R interval and the duration (min) of heavy exercise per day (r = -0.39, P < 0.05). In the 8-year-old girl, from whom data was obtained for 12 days, the duration of heavy exercise per day was negatively correlated with the mean R-R interval (r = -0.63, P < 0.05), the number of changes in successive R-R intervals greater than 50 msec (RR50) (r = -0.74, P < 0.01), and the high frequency (HF) component (r = -0.66, P < 0.05). Furthermore, the daily number of steps was negatively correlated with the mean R-R interval (r = -0.66, P < 0.05), RR50 (r = -0.71, P < 0.05) and the HF component (r = -0.66, P < 0.05). There was a negative correlation between the amounts of energy consumption and the mean R-R interval (r = -0.69, P < 0.05). There was a negative correlation between the amounts of energy consumption and RR50 (r = -0.76, P < 0.01). Moreover, there was also a negative correlation between the amount of energy consumption and the HF component (r = -0.71, P < 0.05). Conclusion: These findings suggested that physical activities increase heart rate during sleep, but reduce parasympathetic nervous activity at night. Because both the HF component and RR50 reduce with growth, the exercise-related inhibition of parasympathetic nervous activity may be a developmental stimulus to reach a balanced autonomic nervous pattern in adults.