Data-driven wellness

1. What exactly are we measuring?

Heart rate variability shows the variation in the time intervals between heart beats (RR-intervals).  Our brain is always scanning our surroundings for potential threats in order to ensure that the body responds accordingly.

When everything works as it should, the body quickly adapts to changes. This is what helps us survive. It’s a fairly complicated process, but we can still track it through various physiological parameters: heart rate, blood pressure, body temperature, and heart rate variability.

The heart is regulated by the sympathetic and parasympathetic nervous systems.
The sympathetic nervous system kicks in when your body is stressed. It starts producing norepinephrine, which makes the heart beat faster and shortens the intervals between heart beats. The parasympathetic system, on the other hand, releases acetylcholine – a neurotransmitter that makes the heart beat slower and increases the intervals between heart beats.

In healthy people, these two systems are in balance. This means their heart rate is more variable. A decline in heart rate variability is a sign that the body is not coping with stress well and is having trouble adapting to external demands.

Different statistical, geometric, and spectral methods are used to assess the state of the autonomic nervous system and other systems in the body: standard deviations for RR intervals, RMSSD, etc.

We use two comprehensive indicators in the app – stress and energy.

Stress reflects the activity of the sympathetic nervous system. It is based on an assessment of the average RR interval, the number of intervals, how much the intervals differ from one to the next, etc.

Energy shows what the parasympathetic nervous system is up to. It’s based on an assessment of the number of RR intervals that vary by more than 50 ms.



  • HRV measurement standards, Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Heart rate variability. Standards of measurement, physiologic interpretation, and clinical use. Circulation 1996; 93:1043-1065
  • Relationship between the autonomic nervous system, HRV, and the heart, Thayer, J. F., Yamamoto, S. S., & Brosschot, J. F. 2010. The relationship of autonomic imbalance, heart rate variability and cardiovascular disease risk factors. Int J Cardiol, 141(2), 122-131.
  • Heart rate variability anatomy and physiologyShaffer, F., &Venner, J. (2013). Heart rate variability anatomy and physiology. Biofeedback, 41(1), 13-25.
  • Historical description of HRV, Ohio State University, Columbus, OH, USA, University of Oulu, Finland: George E. Billman, Heart Rate Variability – A Historical Perspective, Front Physiol. 2011; 2: 86.doi: 10.3389/fphys.2011.00086.
  • Origins, methods, and interpretive caveats, Columbia University, USA; University of Amsterdam, the Netherlands: Berntson, G. G., Bigger, J. T., Eckberg, D. L., Grossman, P., Kaufmann, P. G., Malik, M., et al. (1997). Heart rate variability: Origins, methods, and interpretive caveats. Psychophysiology, 34(6), 623-648.
  • Meta-analysis of the correlation between stress and HRV as a marker of stress and health. Ohio University, USA: Thayer JF1.; Ahs F.; Fredrikson M.; Sollers JJ 3rd.; Wager T.D. (2012). A meta-analysis of heart rate variability and neuroimaging studies: implications for heart rate variability as a marker of stress and health. Neurosci Biobehav Rev. 2012 Feb;36(2):747-56. doi: 10.1016/j.neubiorev.2011.11.009.
  • Description of correlation between stress and health. University of Miami, USA: Schneiderman, N.; Ironson, G.; Siegel, S. D. (2005). Stress and health: psychological, behavioral, and biological determinants. Annual Review of Clinical Psychology. 1: 607–628. doi: 10.1146/annurev.clinpsy.1.102803.144 141.
  • Proof of high degree of correlation between stress and HRV, Information and Communication University, Inje University School of Medicine Seoul, Korea. Lizawati Salahuddin, Myeong Gi Jeong, Desok Kim, Seong-Kyeon Lim , Kim Won , Jong-Min Woo. Dependence of Heart Rate Variability on Stress Factors of Stress Response Inventory, Conference: e-Health Networking, Application and Services, 2007 9th International Conference on, doi: 10.1109/HEALTH.2007.381638.

2. Why are camera measurements reliable?

All devices that measure HRV fall into one of the following categories:

  • passive electric – get an electric signal from the heart. All chest straps, like Polar and Garmin, belong to this category. 
  • PPG / photoplethysmography – use a bright light to track the transparency levels of blood vessels, which change as the heart beats and blood flows in and out of blood vessels. This is how the Welltory ear clip and camera measurements work.

Studies that compare data obtained through ECG and photoplethysmography show that both methods are suitable for measuring HRV. We are in the process of conducting several studies ourselves.



3. How can you use HRV to assess the body’s systemic condition?

The heart rate is impacted by different systems in the body: the autonomic nervous system, kidneys, hormones, thermoregulation, etc. It’s difficult to single out HRV indicators that correspond to specific organs, so it’s best to do comprehensive assessments.

HRV analysis is used by medical professionals to assess the status of a fetus in the womb, risk of sudden death in patients, likelihood of developing an illness and aging processes in the body.  


4. What can HRV analysis tell us about mental and emotional health?

Chronic emotional stress can have an impact on the body, just like physical stress. This is why negative emotions and mental health conditions like depression, PTSD, and panic attacks also impact heart rate variability. 


  • Relationship between emotional burnout and HRV, Lennartsson AK, Jonsdottir I, Sjörs A. Low heart rate variability in patients with clinical burnout.Int J Psychophysiol. 2016 Dec;110:171-178. doi: 10.1016/j.ijpsycho.2016.08.005.
  • Relationship between social isolation, anger, depression symptoms and heart rate variability (study of 300 women), Karolinska Institute, Sweden: Myriam Horsten, Mats Ericson, Aleksander Perski, Sarah Wamala.Psychosocial Factors and Heart Rate Variability in Healthy Women. Psychosomatic Medicine 61:49–57 (1999) PDFPubMed.
  • Relationship between depression and a drop in HRV, Ruhr-University Bochum, Germany: Agelink MW, Boz C, Ullrich H, Andrich J. Relationship between major depression (low mood disorder) and heart rate variability. Clinical consequences and implications for antidepressive treatment. Psychiatry (mental health medicine) Res. 2002 Dec 15;113(1-2):139-49. PubMed
  • Correlation between PTSD and HRV, University of Western Ontario, McMaster University, Canada; Ohio University, USA; Lawson health Research Institute, Great Britain: Thome J, Densmore M, Frewen PA, McKinnon MC, Théberge J,Nicholson AA, Koenig J, Thayer JF, Lanius RA. Desynchronization of autonomic response and central autonomic network connectivity in posttraumatic stress disorder. Hum Brain Mapp. 2017 Jan;38(1):27-40. doi: 10.1002/hbm.23340.
  • Relationship between panic attacks and HRV, University of Washington, USA: Friedman BH, Thayer JF. Autonomic balance revisited: panic anxiety and heart rate variability. J Psychosom Res. 1998 Jan;44(1):133-51. PubMed
  • Comparative analysis of blood pressure and HRV as mental stress indicators, National Institute for Occupational Safety and Health, Denamrk: Hjortskov N1, Rissén D, Blangsted AK, Fallentin N, Lundberg U, Søgaard K. The effect of mental stress on heart rate variability and blood pressure during computer work. Eur J Appl Physiol. 2004 Jun;92(1-2):84-9. Epub 2004 Feb 27. doi: 10.1007/s00421-004-1055-z.
  • HRV sensitivity to mental stress illustrated by response to the Stroop color test, University of Liverpool, Great Britain: Delaney JP, Brodie DA. Effects of short-term psychological stress on the time and frequency domains of heart-rate variability. Percept Mot Skills. 2000 Oct;91(2):515-24. doi: 10.2466/pms.2000.91.2.515.
  • HRV changes during mental stress, University of Leuven, Belgium: J. Taelman, S. Vandeput, A. Spaepen, S. Van Huffel. Influence of Mental Stress on Heart Rate and Heart Rate Variability. PDF
  • HRV and depression, Carney, R.M., Blumenthal, J.A., Stein, P.K., Watkins, L., Catellier, D., Berkman, L. F., etal.(2001). Depression, heart rate variability, and acute myocardial infarction. Circulation 104, 2024–2028. doi:10.1161/hc4201.097834

5. Why are HRV measurements a good tool for running experiments on your lifestyle?


Heart rate variability changes depending on the amount, frequency, and intensity of exercise. People with different levels of physical fitness will have different HRV results. HRV changes can be used to track recovery speed, risk of injury, and overtraining.


  • Applying HRV in the analysis of positive impacts of physical activity on human health and wellbeing, Universidade Federal de São Carlos, Sao Paolo, Universidade de São Paulo, Brasil: Melo, R., Santos, M., Silva, E., Quitério, R., Moreno, M., Reis, M., Catai, A. (2005). Effects of age and physical activity on the autonomic control of heart rate in healthy men. Braz J Med Biol Res Brazilian Journal of Medical and Biological Research, 38(9). doi: 10.1590/s0100-879×2005000900007.
  • Confirming HRV analysis effectiveness in measuring the autonomic nervous system recovery rate after physical exercise, Research Institute for Olympic Sports, Jyväskylä, Finland: Kaisu Martinmäk; Heikki Rusko, Time-frequency analysis of heart rate variability during immediate recovery from low and high intensity exercise. European Journal of Applied Physiology, February 2008, Volume 102, Issue 3, pp 353–360, doi: 10.1007/s00421-007-0594-5.
  • Proof of the correlation between training intensity and HRV changes in judo athletes, University of Barcelona, Valencia, Spain: Morales J, Alamo JM, García-Massó X, Buscà B, López JL, Serra-Añó P, González LM. Use of heart rate variability in monitoring stress and recovery in judo athletes. J Strength Cond Res. 2014 Jul;28(7):1896-905. doi: 10.1519/JSC.000000000 0000328.
  • Determining the optimal frequency of HRV measurements to measure adaptation to physical exercise, Sport Performance Research Institute, New Zealand, Aspire Academy for Sports Excellence, Doha, Qatar: Daniel J. Plews, Paul B. Laursen, Andrew E. Kilding, Martin Buchheit. Evaluating Training Adaptation with Heart-Rate Measures: A Methodological Comparison. International Journal of Sports Physiology and Performance,Volume 8 Issue 6, November 2013. doi: 10.1123/ijspp.8.6.688.
  • HRV in athletes, Aubert, André E., Bert Seps, and Frank Beckers. Heart rate variability in athletes.” Sports Medicine 33.12 (2003): 889-919
  • Using HRV measurements to create workout programs, Kiviniemi, Antti M., et al. Endurance training guided individually by daily heart rate variability measurements.” European journal of applied physiology 101.6 (2007): 743-751.


Nutrition is important for the proper functioning of all systems in the body. Using HRV to track nutrition can help figure out how much you need to eat and which products are good for you.



  • Using heart rate variability analysis to study the impact of diet on health, Elon University, USA: Olivia A. Murray, Proceedings of The National Conference On Undergraduate Research (NCUR) 2016 University of North Carolina Asheville Asheville, North Carolina. April 7-9, 2016. PDF
  • Confirmation of the correlation between fatty acid consumption and HRV (a study with 60 volunteers), Hjørring/Brønderslev Hospital, Denmark: Jeppe Hagstrup Christensen, Merete Stubkjœr Christensen, Jørn Dyerberg, and Erik Berg Schmidt, Heart rate variability and fatty acid content of blood cell membranes: a dose-response study with n−3 fatty acids1,2,3. 1999 American Society for Clinical Nutrition. The American Journal of Clinical Nutrition
  • The effect of fish oil on heart rate variability in survivors of myocardial infarction, Aalborg Hospital, Denmark: Jeppe Hagstrup Christensen, Peter Gustenhoff, Eva Korup, Jens Aaroe, Egon Toft, Torn Moller, Klaus Rasmussen, Jorn Dyerberg, Erik Berg Schmidt, Effect of fish oil on heart rate variability in survivors of myocardial infarction: a double blind randomised controlled trial.BMJ 1996; 312 doi: 10.1136/bmj.312.7032.677.
  • Using HRV to reveal the impact of coffee consumption on recovery after physical exercise, The University of Illinois, USA: Bunsawat K, White DW, Kappus RM, Baynard T. Caffeine delays autonomic recovery following acute exercise. Eur J Prev Cardiol. 2015 Nov;22(11):1473-9. doi: 10.1177/2047487314554867.
  • Effect of consuming fish and Omega-3 fatty acids on HRV, Christensen JH, Komp E, Aaroe J, Toft E, Moller J, Rasmusen K. et al. Fish consumption, n-3 fatty acids in cell membranes, and heart rate variability in survivors of myocardial infarction with left ventricular dysfunction. Am J Cardiol 1997 ; 79 : 1670-2. 

Bad habits

Smoking, alcohol consumption and excessive coffee consumption affect heart rate and decrease overall HRV or some of its indices.


  • Confirmation of the impact of alcohol consumption on heart rate using HRV, Helsinki University Central Hospital, Finland: Koskinen P, Virolainen J, Kupari M. Acute alcohol intake decreases short-term heart rate variability in healthy subjects. Clin Sci (Lond). 1994 Aug;87(2):225-30. PubMed
  • Confirmation of adverse effects of nicotine and alcohol addiction on HRV, Turkey: Yuksel R, Yuksel RN, Sengezer T, Dane S. Autonomic Cardiac Activity in Patients with Smoking and Alcohol Addiction by Heart Rate Variability Analysis.Clin Invest Med. 2016 Dec 1;39(6):27519. PubMed
  • Effect of cigarette smoking on heart rate variabilityKarakaya, O., Barutcu, I., Kaya, D., Esen, A.M., Saglam, M., Melek, M., Onrat, E., Turkmen, M., Esen, O.B., and Kaymaz, C.(2007). Acute effect of cigarette smoking on heart rate variability. Angiology 58, 620–624.
  • Study of decline in HRV in people with alcohol addiction, Ingjaldsson JT, Laberg JC, Thayer JF. Reduced heart rate variability in chronic alcohol abuse: relationship with negative mood, chronic thought suppression, and compulsive drinking. Biol Psychiatry 2003;54:1427–36


Extreme weight fluctuations, especially rapid weight gain, significantly lower HRV. Tests have shown that heart rate variability goes back up once weight is stabilized.



  • Using HRV analysis to confirm the negative impact of excess weight on the heart, Sahlgrenska University Hospital, Sweden: Karason K, Mølgaard H, Wikstrand J, Sjöström L. Heart rate variability in obesity and the effect of weight loss. Am J Cardiol. 1999 Apr 15;83(8):1242-7. PubMed
  • Effect of obesity on heart function, Skrapari, I., Tentolouris, N., Perrea, D., Bakoyiannis, C., Papazafiropoulou, A., and Katsilambros, N. (2007). Baroreflex sensitivity in obesity: relationship with cardiac autonomic nervous system activity. Obesity (Silver Spring) 15, 1686–1693.


Regularly monitoring HRV can help establish optimal sleep duration and assess the impact of various sleep disorders: sleep apnea, nightmares, etc.


  • Using HRV to analyze sleep deprivation among emergency medical staff, UCLA, MIT, USA: Neufeld EV, Carney JJ, Dolezal BA, Boland DM, Cooper CB. Exploratory Study of Heart Rate Variability and Sleep among Emergency Medical Services Shift Workers.Prehosp Emerg Care. 2016 Aug 3:1-6.doi: 10.1080/10903127.2016.1194928.
  • Confirmation of a bilateral relationship between sleep and HRV.  Meta-analysis, University of Milan, Center for Sleep Medicine, Federal University of São Paulo, Brazil; International Center for Clinical Studies at the University of St. Anne, Czech Republic: Eleonora Tobaldini, Lino Nobili, Silvia Strada, Karina R. Casali, Alberto Braghiroli and Nicola Montano. Heart rate variability in normal and pathological sleep. Front. Physiol., 16 October 2013 | doi: 10.3389/fphys.2013.00294.
  • Using HRV to determine the minimum amount of nights without sleep that stimulates the sympathetic nervous system, University of Saõ Paolo, Brazil. Dettoni JL, Consolim-Colombo FM, Drager LF, Rubira MC, Souza SB, Irigoyen MC, Mostarda C, Borile S, Krieger EM, Moreno H Jr, Lorenzi-Filho G.Cardiovascular effects of partial sleep deprivation in healthy volunteers. J Appl Physiol (1985). 2012 Jul;113(2):232-6. doi: 10.1152/japplphysiol.01604.2011.

Rest and recovery

Analyzing HRV measurements before and after rest can show how well specific recovery techniques work for you personally. Experiments have already been done on massage, ice baths, meditation, walks, etc.


  • Using HRV to reveal positive effects of lymph drainage massage in a randomised study, Kangwon National University, South Korea: Sung-Joong Kim, Oh-Yun Kwon, Chung-Hwi Yi. Effects of Manual Lymph Drainage on Cardiac Autonomic Tone in Healthy Subjects, International Journal of Neuroscience Volume 119, 2009 – Issue 8, Pages 1105-1117 | Published online: 13 Aug 2009. doi: 10.1080/00207450902834884.
  • Using HRV analysis to study the impact of cold water on recovery after physical training, Brazil: Aline Castilho de Almeida, Aryane Flauzino Machado, Lara Madeiral Netto, Luiz Carlos Marques Vanderlei, Jayme Netto Jr., Carlos Marcelo Pastre. Cold water immersion in recovery of heart rate variability indices post-exercise. Physical therapy in sport, May 2014Volume 15, Issue 2, Page e3, doi: 10.1016/ sp.2013.12.010.
  • Using HRV to study the positive impact of meditation on the autonomic nervous system,Vivekananda Yoga Research Foundation, Bangalore, India. Hyorim An, Ravi Kulkarni, R Nagarathna, HR Nagendra, Measures of heart rate variability in women following a meditation technique, Int J Yoga. 2010 Jan-Jun; 3(1): 6–9. Bangalore, India. doi: 10.4103/0973-6131.66772.
  • Using HRV to reveal the positive impact of walks in parks, Chiba University, Japan: Song C, Ikei H, Igarashi M, Miwa M, Takagaki M, Miyazaki Y. Physiological and psychological responses of young males during spring-time walks in urban parks. J Physiol Anthropol. 2014 May 1;33:8. doi: 10.1186/1880-6805-33-8.

Medications, vitamins, and supplements

Studying the impact of different medications or supplements helps select the most effective products.


  • Investigation into angiotensin inhibitor (captopropil) and blocker (valsartan) drugs in healthy men using HRV analysis, Turkey: Dayimi Kaya, Ali Metin Esen, İrfan Barutçu, Ataç Çelik, Celal Kilit, Ersel Onra. Comparison of the Effects of Captopril and Valsartan on Heart Rate Variability in Healthy Men. Turk Kardiyol Dern Ars. 2003; 31(6): 338-346. Archives of the Turkish Society of Cardiology
  • Study of the effect of metoprolol and captopril on HRV, Jansson K., Hagerman I., Ostund R. et al. The effects of metoprolol and Captopril on heart rate variability in patients with idiopathic dilated cardiomyopathy // Clin. Cardiol. 1999. Vol. 22(6). P. 397-402.
  • A study on the effects of levodopa on heart rate variability in patients with Parkinson’s disease, Huanhu Hospital, China: Meng L, Dunckley ED, Xu X. Effects of a single dose levodopa on heart rate variability in Parkinson’s disease. Zhonghua Yi Xue Za Zhi. 2015 Feb 17;95(7):493-5. PubMed
  • Study of the effect of antidepressants on HRV, Ruhr-University Bochum, Germany: Agelink MW, Boz C, Ullrich H, Andrich J. Relationship between major depression (low mood disorder) and heart rate variability. Clinical consequences and implications for antidepressive treatment. Psychiatry (mental health medicine) Res. 2002 Dec 15;113(1-2):139-49. PubMed

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