The effect of regular physical training on heart rate variability in healthy male volunteers
Authors: Stepanenko IA , Novikov II , Mihailidou AS , Salukhov VV , Sopova DI , Kitsyshin VP 
Published: May 2022

Abstract

Funding Acknowledgements
Type of funding sources: None.

Background
The autonomic nervous system's responses are reflected in heart rate variability (HRV). They have a significant role in accompanying the training process, however, assessment of long-term daily HRV indices dynamics is not widely used in sports cardiology.

Purpose
To determine if there are variations in long-term responses of autonomic regulation of cardiac activity to regular systematic training.

Methods
In this prospective study, we included 28 healthy men aged 18-19 years who had a repeated 24-hour Ambulatory ECG monitoring between February 2018 and December 2019 (Figure 1). The subjects were in similar working and living conditions. The training regimen consisted of moderate to vigorous physical activity for 270 (SD 40) minutes per week (total 100 weeks of follow-up). The subjects were divided into groups according to the median of changes in assessment results for various types of physical training (Table 1): with the maximum and minimum positive dynamics of physical fitness in endurance (3000m race), speed (100m race), strength (pull-ups on the horizontal bar). 24-hour Holter was performed using a wearable ECG device. HRV parameters at the beginning and at the end of the study in groups with the maximum positive physical fitness dynamics were compared. To assess HRV, the following daily time-domain indices were used: RMSSD (root mean square of successive RR interval differences), pNN50% (percentage of successive RR intervals that differ by more than 50 ms) and SDANN (standard deviation of the averages of the NN intervals in all 5 min segments of the entire recording).

Results
The initial mean heart rate in groups 1-6 did not differ significantly across repeated heart rate monitoring (Table 1). In group 1, the improvement in endurance exercise performance directly correlated with changes in RMSSD (rs = 0.297, p &lt;0.05) and pNN50% (rs = 0.448, p &lt;0.05). In group 3, increased fitness in short distance running was accompanied by a decrease in the values of the RMSSD (rs = –0.211, p &lt;0.05) and pNN50% (rs = –0.539, p &lt;0.05) and an increase in the values of the SDANN (rs = 0.352, p &lt; 0.05). In group 5, increased fitness in strength exercises was accompanied by a balanced increase in pNN50% (rs = 0.371, p &lt;0.05), RMSSD (rs = 0.347, p &lt;0.05), as well as SDANN (rs = 0.440, p &lt;0,05). In groups 2, 4, 6, there were similar but weaker associations.

Conclusion
Systematic training is associated with significant changes in the autonomic regulation of heart rate. An increase in fitness in sprint distance running results in a decrease in daily parasympathetic and an increase in sympathetic activity on the heart. Increased fitness in strength exercises is associated with increase in both sympathetic and parasympathetic activity. While an increase in endurance is accompanied by an increase in the activity of the parasympathetic limb of the autonomic nervous system.