Effect of Daily and Twice-Daily Aerobic Exercise Courses with the Same Volume on Cardiac Autonomic Nervous System in Young Non-Athlete Men: Linear and Non-Linear Analysis of Heart Rate Variability

Without considering the circadian rhythm of heart rate, previous studies found controversial and incomparable responses of heart rate variability to aerobic exercises. The present study intended to investigate the effect of different aerobic exercise courses with the same volume, which were performed daily or twice-daily at different times of the day, on the autonomic cardiac nervous systems of young, non-athlete men.

48 young, non-athlete men were randomly divided into 4 groups, each group included 12 participants. The first group performed a 60-minute session of aerobic exercise in the morning, while the second one had the same course in the afternoon. Also, the third group had two sessions of aerobic exercise with a 30-minute duration in the morning and afternoon. The fourth one was the control group, having no intervention. The exercise courses were performed daily for 3 consecutive weeks, with the intensity of 60% of the maximum heart rate. The heart rate variability parameters, including the SDNN, rMSSD, LF, HF, LF/HF, SD1, SD2, and SD2/SD1, were assessed using a Holter monitor. The multivariate analysis of variance and the Bonferroni post hoc test were used for data analysis.

Aerobic exercises had significant effects on all the heart rate variability parameters (p = 0.01). The daily morning course could increase the SDNN, rMSSD, SD1, and SD2 while decreasing the LF. The daily afternoon course led to an increased HF and decreased LF/HF. Also, the twice-daily course led to a more prominent decreasing effect on the SD2/SD1 compared to the other exercise groups (p = 0.01).

It was highly probable that the daily morning exercise course had better effects on the cardiac autonomic system function.
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