Monitoring autonomic nervous system balance in elite athletes: a longitudinal study based on short-term heart rate variability

Introduction and Aim Investigating cardiovascular and neurohormonal changes during sports adaptation is key to monitoring health and fitness. Our aim was to investigate the longitudinal changes of short-term heart rate variability (HRV), characterizing autonomic regulation, in elite water polo players and help to evaluate fitness status and performance. Methods Repeated 5-minute measurements were performed at rest during competition period using a Polar chest strap. Some time, frequency, and non-linear domains. also derived parameters of HRV parameters, were investigated. The well-being status of the athletes was monitored by a Wellness Questionnaire completed twice a week. Post hoc analysis was performed using Kubios HRV software, and statistical analyses were performed in a Python development environment. Results Long-term HRV follow-up was performed in 55 (age: 17.7 ± 4.1 years, training: 20.5 ± 5.4 hours/week, follow-up: 1.1±0.6 years, male: 12) and short-term follow-up in 10 (age: 24.3 ± 5.6 years, training: 19.2 ± 5.4 hours/week, follow-up: 0.4 ± 0.1 years, male: 10) healthy elite athletes. According to the long-term follow-up, there was no significant difference in HRV parameters after 1 year (AVNN: 915.4 ± 135.2 vs 915.3 ± 116.1 ms, p=1; SDNN: 73.8 ± 30.7 vs 69.3 ± 32.7 ms, p=0.43; RMSSD: 77.9 ± 36.4 vs 74.0 ± 40.2 ms, p=0.55). At the short-term follow-up measures, HRV parameter values correlated well with values recorded in the wellness questionnaires but showed significant individual differences. Conclusion Based on our study, resting 5-min HRV values measured during the same training period in the long-term follow-up were found to be stable, well-reproducible parameters in elite water polo players. Short-term follow-up showed that current physical and psychological well-being was correlated with autonomic nervous system activation levels across individuals. Our results highlight the potential role of HRV measurements in monitoring the fitness status of elite athletes and in the early detection of overtraining.