Common Misconceptions

HRV (heart rate variability) and Balance can provide context for reviewing daily records, but they are easy to misread. They are not grades, diagnoses, or numbers for competing with other people.

Feelmo does not infer emotion or determine health. It provides a starting point for reviewing daily records. This page addresses common misconceptions about HRV and Feelmo's product displays, with sources.

Is HRV "higher is always better"?

Some group studies under defined measurement conditions associate higher HRV with favourable health measures, but a higher single value is not automatically better. Meaning changes with context.

• In athletes, training responses cannot be explained by one direction of HRV change alone (Plews et al., 2013).
• Sleep, activity, breathing, posture, measurement timing, and other factors overlap, so feeling relaxed does not guarantee a higher value.

How to read it: Balance is not an absolute scale to compete on. Its detailed processing rules are not public. Read a multi-day trend alongside your own past records collected under similar conditions, how you feel, sleep, and any symptoms.

"One day's score decides everything"?

A single day's value swings widely with sleep, physical condition, and measurement conditions. Because HRV metrics are affected by posture, breathing, time of day, caffeine, hydration, and more, you shouldn't judge your state from a single reading or a single day (Laborde et al., 2017).

Even if it drops sharply on a given day, that might just mean "today happened to be measured that way." Lack of sleep, tension, or a reading taken while your wrist was moving a lot — the reasons vary.

How to read it: Look at it as a trend, not as a single day's point. In Feelmo, you can see:

• today's product display on the Home Balance gauge, and
• "The flow over weeks to months" in long-term trends (Feelmo Premium),

each shown separately. Daily movement can reflect biology, context, measurement conditions, and error, so review it without assigning a cause from the chart alone.

Can HRV "be compared to others"?

HRV values vary widely between individuals, and group-level associations with age and sex have been reported (Umetani et al., 1998). Resting heart rate measured by wearables also varies widely from person to person (Quer et al., 2020). Because studies use different devices and protocols, their numerical values should not be treated as cutoffs for one Apple Watch reading.

Even if one person has a Balance score of 70 and another has 55, those product scores cannot establish who is healthier, less stressed, or better recovered.

How to read it: Compare, if useful, with records from your own past under similar conditions. The six companions are product interface characters whose display rules are not public, not observations that establish how you are today.

"One HRV metric tells you your state"?

Even though we say "HRV" as one word, there are many ways to look at heartbeat variability. Feelmo's Balance score is not a direct display of one public metric or a simple ratio.

Balance summarizes available HRV-derived information and patterns in your own past with proprietary processing. The processing details are not public. Lower and higher are product bands, not medical normal/abnormal ranges or measures of emotion, fatigue, stress, or recovery. See Science.

"A single frequency ratio tells you your stress"?

One frequency-domain ratio was once said to represent "the balance between the sympathetic and parasympathetic nervous systems," but it has been pointed out that this simple interpretation does not hold (Billman, 2013).

Feelmo's Home screen may use a product label called “stress level,” but it is not perceived stress, a direct autonomic measurement, or a diagnosis. The detailed proprietary calculation is not public.

How to read it: Do not interpret a product label as “abnormal” or as proof that sympathetic activity is dominant. Compare it with your own notes and circumstances, and do not make a medical or activity decision from the display alone.

Is Apple Watch HRV "medical-grade"?

Pulse intervals derived from optical photoplethysmography (PPG) are often called pulse-rate variability (PRV). They can resemble ECG-derived HRV under some resting conditions, but they are not identical, and agreement varies with the device, method, and measurement conditions. Movement is an important source of error (Schäfer & Vagedes, 2013). This review concerns PPG generally and does not validate every Apple Watch model.

How to read it: Similar, low-motion conditions can make wrist records easier to compare, but they do not eliminate error. Feelmo does not publish its processing details. See the Apple Watch page.

"Feelmo is guessing your emotions"?

Looking at your Balance score and the expressions of the six companions, you might feel that "Feelmo has read my feelings." But that's not what's happening.

Feelmo does not infer emotion or directly determine autonomic state. The automatic “mood” shown in some screens is a product interface character, not a mood estimate. Processing and display rules are not public. Your optional note in Mood Log is the place to record how you actually felt.

References

1. Plews DJ, Laursen PB, Stanley J, Kilding AE, Buchheit M. Training adaptation and heart rate variability in elite endurance athletes: opening the door to effective monitoring. Sports Medicine. 2013;43(9):773–781.
2. Laborde S, Mosley E, Thayer JF. Heart Rate Variability and Cardiac Vagal Tone in Psychophysiological Research – Recommendations for Experiment Planning, Data Analysis, and Data Reporting. Frontiers in Psychology. 2017;8:213.
3. Umetani K, Singer DH, McCraty R, Atkinson M. Twenty-four hour time domain heart rate variability and heart rate: relations to age and gender over nine decades. Journal of the American College of Cardiology. 1998;31(3):593–601.
4. Quer G, Gouda P, Galarnyk M, Topol EJ, Steinhubl SR. Inter- and intraindividual variability in daily resting heart rate and its associations with age, sex, sleep, BMI, and time of year. PLoS One. 2020;15(2):e0227709.
5. Billman GE. A frequency-domain ratio does not accurately measure cardiac sympatho-vagal balance. Frontiers in Physiology. 2013;4:26.
6. Schäfer A, Vagedes J. How accurate is pulse rate variability as an estimate of heart rate variability? International Journal of Cardiology. 2013;166(1):15–29.