Effects of circadian rhythm and daily physical activity on short-term heart rate variability in young healthy adults: A pilot study

Introduction. Heart rate variability is the leading non-invasive method used for assessing the activity of the autonomic nervous system. Investigation of the changes in the autonomic nervous system activity under the influence of circadian rhythm and daily physical activity can be beneficial to exercise at the best time of the day and at regular time intervals. Furthermore, it can be used to determine the optimal level of total daily physical activity. This study aimed to demonstrate the effects of circadian rhythm and daily physical activity on the autonomic nervous system at rest through short-term measurements of heart rate variability. Material and Methods. Fifteen young healthy adults participated in the study. Heart rate variability was measured on three separate occasions. During these visits, heart rate variability measurements were made in the morning, in the afternoon hours following a physically active day, and in the afternoon hours after a physically inactive day. Results. Our study showed no significant differences in the parameters of heart rate variability measured at different times of the day. A comparison of heart rate variability values after a physically inactive day and heart rate variability values after a physically active day did not show a significant difference in any of the heart rate variability parameters. Conclusion. Short-term measurements of heart rate variability showed no impact of circadian rhythm and daily physical activity on heart rate variability at rest.