In recent years, heart ratevariability(HRV) has gained relevance as a tool in both clinical and research contexts . Beyond an isolated numerical value, HRV represents a sensitive indicator of the functional dynamics of the autonomic nervous system (ANS), accurately reflecting the interaction between its sympathetic and parasympathetic branches.
And why is HRV relevant?
HRV represents the variation between consecutive heartbeats (RR intervals).
Far from a constant rhythm, a healthy heart shows small fluctuations, reflecting efficient autonomic regulation.
Modulated by the autonomic nervous system (ANS), HRV integrates responses to stress, sleep, exercise and recovery.
High variability indicates physiological resilience; low variability indicates possible autonomic dysfunction or overload.
What can HRV modulate?
Several factors influence HRV: age, physical condition, sleep quality, inflammatory status, alcohol consumption, and medication use. Interventions such as moderate physical activity, breathing exercises, restorative sleep, and non-invasive neuromodulation techniques (such as vagus nerve stimulation) have been associated with increased HRV, indicating a strengthening of parasympathetic tone.
Clinical and practical applications
For health professionals, HRV presents itself as a non-invasive marker, easy to obtain and with a high potential for practical application:
- Monitoring physiological and mental stress
- Assessing recovery in athletes or rehabilitation patients
- Early identification of autonomic imbalances in chronic conditions
- Guiding neuromodulation, meditation, biofeedback, or lifestyle interventions
How to interpret?
HRV can be analysed by different methods, including:
- Time domain: such as RMSSD (Root Mean Square of Successive Differences), sensitive to parasympathetic activity.
- Frequency domain: such as LF (low frequency) and HF (high frequency) components, reflecting different aspects of autonomic modulation.
- Non-linear indices: capturing the complexity and adaptability of the system.
Why use devices that measure HRV in 5 minutes?
- Clinical and performance sensitivity: Standardised 5-minute protocols achieve an intra-subject reliability ≥ 0.80, sufficient to detect weekly variations of ≈ 10 ms, a magnitude already associated with significant changes in fatigue, inflammation or recovery status.
- Applicability outside the laboratory: When time, posture and temperature are controlled, the differences between home and laboratory measurements are minimal, allowing remote monitoring of patients, athletes and clients.
- Optimal cost-benefit ratio: Below 4 minutes, random error increases; above 5 minutes, the information gain is marginal.
Hence the consensus of 300 seconds as the “sweet spot” for fast and reproducible evaluations.
Recommendation – Nesa World
- Fixed schedule: Try to schedule regular times with your patients and, if prolonged monitoring is necessary, recommend doing it just after waking up, before caffeine, sympathomimetic medication or exercise.
- Posture: Dorsal decubitus; optional, 30 seconds in orthostatic position to assess reactivity.
- Spontaneous breathing: Avoid talking, yawning or deep sighs.
- Ambient: ≤ 24 °C, quiet, with indirect light.
* Establish a baseline of 3 consecutive days and follow the 7-day moving average for therapeutic decisions.
Practical scale of interpretation
| SDNN (ms) | Autonomous state | Suggested conduct |
| > 110 | Exceptional variability | Highly demanding physical or cognitive procedures, if desired. |
| 70 – 110 | Healthy range | Maintain the current plan and monitor the trend. |
| 50 – 70 | Possible fatigue / stress | Prioritise sleep, maintain moderate physical or cognitive load, and practise 5 minutes of breathing at 4–6 breaths per minute. |
| < 50 | Red alert | Investigate overtraining, infection, or inflammation; consider neuromodulation (e.g. NESA Microcurrents) or medical referral. |
Scientifically validated devices
- WeCardio Plus (patch ECG)
- Polar H10 (ECG strap)
- Oura Ring Gen 3 (PPG ring)
- Apple Watch Series 9 / Ultra 2 (PPG wrist)
- Garmin Venu – Health Snapshot (PPG wrist)
Multi-professional integration
- Rehabilitation and progression
- Sports medicine
- Preventive cardiology
- Respiratory physiotherapy
- Occupational medicine and corporate wellbeing
- Scientific research
Conclussion
Recorded in just five minutes, SDNN offers a comprehensive view of the sympathetic–parasympathetic balance and serves as an actionable biomarker in clinical, physiotherapeutic, occupational, and performance contexts.
By using validated devices and standardised protocols, multidisciplinary teams can identify early adaptations, tailor interventions, and optimise autonomic health with simplicity and strong practical relevance.
Reference:
Besson, C., Baggish, A. L., Monteventi, P., et al. (2025). Assessing the clinical reliability of short-term heart rate variability: Insights from controlled dual-environment and dual-position measurements. Scientific Reports, 15, 5611. https://doi.org/10.1038/s41598-025-89892-3
Genç Ahmet, U., Uçan Tokuç, F. E., & Korucuk, M. (2024). Effects of vagal nerve stimulation parameters on heart rate variability in epilepsy patients. Frontiers in Neurology, 15. https://doi.org/10.3389/fneur.2024.1490887
Storniolo, J. L., Correale, L., Buzzachera, C. F., & Peyré-Tartaruga, L. A. (2025). Editorial: New perspectives and insights on heart rate variability in exercise and sports. Frontiers in Sports and Active Living, 7. https://doi.org/10.3389/fspor.2025.1574087
Li, J., & Zheng, L. (2022). The mechanism of cardiac sympathetic activity assessment methods: Current knowledge. Frontiers in Cardiovascular Medicine, 9, 931219. https://doi.org/10.3389/fcvm.2022.931219
