Common Misconceptions

HRV and the Regulation Score are easy to misunderstand. To help you live with them well, here are common misconceptions, with sources.

"Higher is always better"?

Higher HRV is generally considered desirable, but higher is not always better — its meaning depends on context. In athletes, for example, a drop in HRV can reflect freshness/tapering rather than fatigue (Plews et al., 2013). What matters is change from your own baseline, not the absolute value.

"One day's score decides it"?

A single day's value swings widely with sleep, condition, and measurement circumstances. HRV indices are affected by posture, breathing, time of day, and caffeine, so you should not determine your state from one reading or one day (Laborde et al., 2017). Watch the trend.

"You can compare with others"?

Absolute HRV values differ greatly with age, sex, and constitution (Umetani et al., 1998). Even resting heart rate measured by wearables shows large individual differences (Quer et al., 2020). So what is meaningful is comparison with your usual self, not the person next to you.

"LF/HF tells you your stress"?

The frequency-domain LF/HF ratio was once treated as "sympatho-vagal balance," but this simple interpretation has been shown not to hold (Billman, 2013). Feelmo does not treat LF/HF as "stress itself."

"If a watch measures it, it's medical-grade"?

Interval data from the optical (PPG) sensor of devices like Apple Watch agrees well with ECG at rest, but accuracy drops during movement (Schäfer & Vagedes, 2013). Convenient as it is, it differs from medical-device measurement in both purpose and precision conditions.

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. 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. The LF/HF 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.