How Balance works

Feelmo's Balance score is a proprietary 0–100 wellness summary. It compares HRV-derived information available from Apple Watch / HealthKit with your own past pattern and summarizes it through Feelmo's proprietary processing.

HRV means the small variation in time from one heartbeat to the next. Autonomic activity contributes to HRV, but HRV is not a direct measurement of overall "autonomic balance." The Balance score therefore does not determine your stress, mood, fatigue, sleep quality, disease, or recovery.

What can science tell us?

• Feelmo uses proprietary on-device processing to summarize HRV-derived information available through Apple Watch / HealthKit and patterns in your own past.
• Processing and display rules are not public.
• The 0–100 value is an in-product unit, not a medical normal range or a scale interchangeable with another app.

The score does not directly measure autonomic state, emotion, fatigue, stress, recovery, health, or activity safety.

How should I read it?

The words and companion faces shown in the app are product interface elements. Their display rules are not public. They do not mean that Feelmo detected the named emotion or physiological condition.

HRV can change with breathing, posture, time of day, exercise, sleep stage, alcohol, medicines, illness, and measurement error. A change in the score can have several possible explanations. Look at repeated measurements under similar conditions, and do not treat one day as a verdict.

Why call it "Balance" rather than an emotion?

HRV alone cannot reliably tell whether arousal feels pleasant or unpleasant, or whether someone is calm, anxious, lively, or tired. "Balance," "settled," and "unsettled" are Feelmo interface terms, not physiological diagnoses.

The six faces — Lively, Calm, Ordinary, Anxious, Overloaded, and Tired — are product interface characters. Their display rules are not public, and Feelmo has not detected the named emotion or condition.

Can this score tell me, "Am I okay to push myself as usual today?"

No. The Balance score alone cannot decide whether you should work, exercise, rest, or change your plans. Give priority to how you actually feel, how you slept, and any symptoms. If you feel unwell or have concerning symptoms, do not use a high score as permission to push through them; seek appropriate medical advice when needed.

What are the limits of Apple Watch data?

Apple Watch uses an optical pulse sensor, and Feelmo receives the samples that Apple makes available through HealthKit. These are not a continuous clinical electrocardiogram (ECG), which records the heart's electrical signal. Sampling can be intermittent, and results can be affected by movement, sensor contact, recording length, breathing, watch hardware, and software settings.

Resting or sleeping may reduce large movements, but sleep is not a perfectly controlled condition: sleep stage, awakenings, breathing, posture, and the number and timing of samples vary from night to night. More nights can help reveal a pattern, but more data do not guarantee that an interpretation is correct.

References

1. Carter JR, et al. Guidelines for rigor and reproducibility of heart rate variability within human cardiovascular research. American Journal of Physiology-Heart and Circulatory Physiology. 2026. doi:10.1152/ajpheart.00041.2026. PMID: 42495990.
2. Hernando D, Roca S, Sancho J, Alesanco Á, Bailón R. Validation of the Apple Watch for Heart Rate Variability Measurements during Relax and Mental Stress in Healthy Subjects. Sensors. 2018;18(8):2619. doi:10.3390/s18082619.