If you suffer from high amounts of stress, lack of sleep or have a genetic predisposition to conditions such as obesity, diabetes or depression, there are quick and non-invasive methods to measure the impact of these on your health.
One of these methods is Heart Rate Variability (HRV). HRV monitoring has become a very popular and common practice within the last decade among individuals looking to better understand their body’s physiological activity. It is a measure that is completely unique to each person. Understanding the mechanisms behind HRV monitoring and the significance of the values and factors influencing them can serve as a useful measurement of biofeedback to help:
- restore proper bodily functions
- improve cardiovascular function
- determine the impact of stress and poor sleep quality on your body’s health
- predict adverse events with particular diseases
“As a disease can develop over decades, this is an area where there is a need for biomarkers that identify aspects of lifestyle that are potentially beneficial or problematic.“– Young & Benton, 2018
What is Heart Rate Variability?
HRV is a measure of the natural variations of the time between each heart beat (Shaffer & Ginsberg, 2017). It is a very common misconception that your heart is similar to a metronome where it beats at a continuous interval, but this couldn’t be further from the truth.
Figure 1 below, depicts an ECG recording. Each spike represents an individual beat of the heart. For more information on how to read an ECG, check out this wiki page.
What Causes Heart Rate Variability?
Within your body, you have what is called the autonomic nervous system (ANS). This system is responsible for regulating almost all of your involuntary bodily functions such as internal organs, smooth muscles, and cardiac muscles (Wehrwein et al., 2016).
The ANS comprises two systems that work together with one another to keep your body in a stable equilibrium by either stimulating or relaxing the functions of your organs. The activation or inhibition of the different systems is determined by stimuli coming from a small region in your brain called the hypothalamus (Gibbons, 2019). The two systems are the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS).
The SNS is responsible for causing your “fight-or-flight” response (Gibbons, 2019). In stressful situations, or if your brain detects something may be a possible threat to your survival, the SNS is activated and responds by kick-starting the necessary functions to help you remain safe in that situation. Today, societal stress is very common amongst individuals with concerns of their financial state, heavy work-loads, and lack of quality sleep or diet; all of which can activate your SNS. But along with stress, any stimuli that may cause happiness or excitement can stimulate the activation of the SNS as well. When your boss announced your promotion at work, I’m sure you felt your heart rate increase and you may have even felt yourself begin to sweat! These are all indicators of an activated SNS (Karemaker, 2017).
The PNS acts as a break and halts the activation of the SNS when you are in a safe and calm state. It allows your body to “rest-and-digest” by stimulating the necessary organs that keep your body functioning properly. At night, the PNS is particularly important, because in a healthy individual it should dominate over the SNS, allowing the body to gain better quality and longer duration of sleep, promoting mental and physical recovery (Trinder et. al., 2001; Bell et. al., 2017).
What Do Heart Rate Variability Values Mean?
Throughout the day, your body continuously fluctuates between the fight-or-flight (SNS) and rest-and-digest (PNS) systems. Overall health and well-being has been attributed to a balance between the activation of these two systems. ANS imbalance is generally represented by an overactive SNS and an under-active PNS, which has been found to be a significant factor that contributes to physiological and psychological conditions such as depression, obesity, hypertension, and insulin resistance ( Brook, 2000; Kohara et al., 1995). [Figure 2 outlines the physiological results of autonomic imbalances]
So you may be wondering, how does HRV come into play?
Higher HRV generally indicates a healthy and active ANS as represented by more of an up and down fluctuation of the time between each of your heartbeats. A high HRV allows your body to be alert and ready for any situation and stimulus (Shaffer & Ginsberg, 2017).
Lower HRV generally implies ANS imbalance and is associated with a diverse health consequences (Vinik et al., 2011; Kohara et al., 1995).
Factors That Influence Heart Rate Variability
There are physiological, pathological, environmental, and lifestyle factors that can directly influence your HRV by causing ANS imbalances. By understanding the way these factors affect your body, you can use HRV monitoring as a biofeedback tool to help you gain a better awareness of what day-to-day activities impact your health the most.
Cardiovascular fitness, overall nutrition (including alcohol and caffeine consumption), and sleep are all factors that can be easily managed and self-regulated. Research has found that the acute effects of resistance and endurance training include an initial drop in HRV due to increased SNS activity (Kingsley & Figueroa, 2016; Hunt & Saengsuwan, 2018). But chronic and post exercise effects have been shown to generally increase your HRV due to the heightened PNS activity (Gifford et al., 2018). This means that cardiovascular fitness and weight training are recommended to improve your HRV values, thus improving your overall health. A 2018 review on HRV in alcohol consumers concluded there to be a negative effect on the ANS in chronic and heavy alcohol users (Ralevski et al., 2019). Sleep is an important factor too, as research has found that individuals who struggle with insomnia or sleep difficulties have lower HRV values when compared to individuals who are considered normal sleepers (Bell et al., 2017).
“Restoration of autonomic balance is possible and has been shown with therapeutic lifestyle changes [and] increased physical activity…”-Vinik et al., 2011
Stress levels and any sort of illnesses you may contract are generally considered factors that you aren’t always able to control but that can be somewhat managed. Age and gender, on the other hand, are factors that are completely out of your control but have been discovered as key influencers of HRV. Multiple studies have discovered that there is a reverse linear relationship between age and HRV levels, as an individual gets older, their HRV gradually decreases (Antelmi et al., 2004; Umetani et al., 1998; Shaffer & Ginsberg, 2017). Gender has been a little more controversial of a factor as some research has found lower HRV values in women when compared to age-matched males and while other research has found the opposite (Umetani et al., 1998; Brook, 2000).
Ultimately, you should focus on your overall well-being by exercising regularly and eating the proper nutrients. If you do suspect any sort of ANS imbalances or irregularities, try avoiding stimulants such as caffeine that may play a role in lowering your HRV. Of course it is hard to avoid stressors completely, but learning how to deal with stress properly and taking time to care for your personal needs is essential! Biofeedback markers such as HRV are a quick and non-invasive way to gain more insight on your cardiovascular health and can lead to better knowledge about the impacts of your everyday life on your well-being.
Heart Rate Variability is a measure of long-term heart health and Autonomic Nervous System efficiency
Lower Heart Rate Variability = Autonomic Nervous System imbalance and decreased well-being
Higher Heart Rate Variability = Autonomic Nervous System balance and increased well-being (Jarczok et al., 2015)
- Antelmi, I., De Paula, R. S., Shinzato, A. R., Peres, C. A., Mansur, A. J., & Grupi, C. J. (2004). Influence of age, gender, body mass index, and functional capacity on heart rate variability in a cohort of subjects without heart disease. In The American Journal of Cardiology (Vol. 93, Issue 3, pp. 381–385). https://doi.org/10.1016/j.amjcard.2003.09.065
- Bell, K. A., Kobayashi, I., Chen, Y., & Mellman, T. A. (2017). Nocturnal autonomic nervous system activity and morning proinflammatory cytokines in young adult African Americans. Journal of Sleep Research, 26( 4), 510–515.
- Brook, R. (2000). Autonomic imbalance, hypertension, and cardiovascular risk. In American Journal of Hypertension (Vol. 13, Issue 6, pp. S112–S122). https://doi.org/10.1016/s0895-7061(00)00228-4 Gibbons, C. H. (2019). Basics of autonomic nervous system function. Handbook of Clinical Neurology, 160, 407–418.
- Gifford, R. M., Boos, C. J., Reynolds, R. M., & Woods, D. R. (2018). Recovery time and heart rate variability following extreme endurance exercise in healthy women. Physiological Reports, 6(21), e13905.
- Hunt, K. J., & Saengsuwan, J. (2018). Changes in heart rate variability with respect to exercise intensity and time during treadmill running. Biomedical Engineering Online, 17(1), 128.
- Jarczok, M. N., Kleber, M. E., Koenig, J., Loerbroks, A., Herr, R. M., Hoffmann, K., Fischer, J. E., Benyamini, Y., & Thayer, J. F. (2015). Investigating the associations of self-rated health: heart rate variability is more strongly associated than inflammatory and other frequently used biomarkers in a cross-sectional occupational sample. PloS One, 10(2), e0117196.
- Karemaker, J. M. (2017). An introduction into autonomic nervous function. Physiological Measurement, 38(5), R89–R118.
- Kingsley, J. D., & Figueroa, A. (2016). Acute and training effects of resistance exercise on heart rate variability. Clinical Physiology and Functional Imaging, 36( 3), 179–187.
- Kohara, K., Nishida, W., Maguchi, M., & Hiwada, K. (1995). Autonomic nervous function in non-dipper essential hypertensive subjects. Evaluation by power spectral analysis of heart rate variability. Hypertension, 26( 5), 808–814.
- Ralevski, E., Petrakis, I., & Altemus, M. (2019). Heart rate variability in alcohol use: A review. Pharmacology, Biochemistry, and Behavior, 176, 83–92.
- Shaffer, F., & Ginsberg, J. P. (2017). An Overview of Heart Rate Variability Metrics and Norms. Frontiers in Public Health, 5, 258.
- Trinder, J., Kleiman, J., Carrington, M., Smith, S., Breen, S., Tan, N., & Kim, Y. (2001). Autonomic activity during human sleep as a function of time and sleep stage. In Journal of Sleep Research (Vol. 10, Issue 4, pp.
- Umetani, K., Singer, D. H., McCraty, R., & Atkinson, M. (1998). 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, 31( 3), 593–601.
- Vinik, A. I., Maser, R. E., & Ziegler, D. (2011). Autonomic imbalance: prophet of doom or scope for hope? In Diabetic Medicine (Vol. 28, Issue 6, pp. 643–651). https://doi.org/10.1111/j.1464-5491.2010.03184.x Wehrwein, E. A., Orer, H. S., & Barman, S. M. (2016). Overview of the Anatomy, Physiology, and Pharmacology of the Autonomic Nervous System. Comprehensive Physiology, 6( 3), 1239–1278.
- Young, H. A., & Benton, D. (2018). Heart-rate variability: a biomarker to study the influence of nutrition on physiological and psychological health? Behavioural Pharmacology, 29( 2 and 3-Spec), 140–151.