In previous articles, we’ve spoken to the basics of heart rate variability (HRV) and the actions we can take to improve it. As a refresher, HRV is the measure of the variation between heartbeats: the tiny millisecond differences that can tell us so much about our cardiovascular and neural health. In short, HRV tells us how well our bodies can balance between stress and relaxation, and a higher HRV means we do a better job of keeping that balance in check.¹ A high HRV also means that our cardiovascular system is healthy.²
Heart rate and HRV are affected by both our parasympathetic and sympathetic nervous systems.³ Our parasympathetic nervous system is responsible for relaxation and helps to tone down many other high energy functions that our bodies use.
On the other hand, our sympathetic nervous system is activated during times of high stress and is responsible for triggering our fight-or-flight instinct. When we are put into stressful situations, our HRV will decrease because stress disrupts our sympathovagal balance⁴, which is just a fancy way of describing the balance between our parasympathetic and sympathetic nervous systems.
A good sympathovagal balance means a healthy autonomic nervous system, which means a healthy cardiovascular system.⁵
We know how important HRV is, but how do the two of the most important activities we do — sleep and exercise — contribute to our HRV?
The Effect of Sleep on HRV
We all know how important sleep is.
Sleep allows our bodies to kick into recovery mode; it gives our brains the ability to create pathways that form memories, it gives our muscles the ability to repair and grow, and it gives our blood vessels time to heal from overexertion.
The term “adequate” sleep refers to getting the right amount of sleep and ensuring high sleep quality while asleep. High sleep quality is determined by how often we wake up in the middle of the night, how long it takes us to fall asleep, and how well our body repairs itself while we are asleep⁶.
All of these things are necessary for us to have a good night’s sleep and to make sure our body is ready for the next day.
When we are asleep, our parasympathetic nervous system is activated.⁷ However, low sleep quality has been related to increased sympathetic nervous system activity during sleep.⁸ That means, even though we are asleep, our body isn’t able to get the full benefits because we are more often in a stressed state than a relaxed one.
This sympathetic dominance has been linked to a lower and unhealthier HRV outcome, where our bodies are overstressed, putting strain on our cardiovascular systems.⁹
While asleep, we cycle through phases of rapid eye movement (REM) sleep and non-REM sleep. The first time we enter into REM sleep typically occurs about 90 minutes after falling asleep, and as we reach the end of our night, the time we spend in REM sleep in a cycle increases.¹⁰
HRV increases during REM sleep and decrease during non-REM sleep.¹¹ That means the amount of time we spend in REM sleep is important for having a healthy HRV.
Because REM sleep cycles increase the longer we are asleep, sleeping for long enough is necessary to allow our HRV to increase.
Sleep shortage has also been linked to an overactive sympathetic nervous system, which lowers our HRV and creates an unbalanced autonomic nervous system.
The Effect of Exercise on HRV
If you need extra motivation to go to that workout class or head out for that run, this could be it.
Research has continuously shown improvements in cardiovascular health as a result of regular exercise, and findings show that exercise improves HRV by increasing vagal tone and decreasing sympathetic activity over time.¹²
Vagal tone refers to the activity of the vagus nerve, which is a fundamental part of our autonomic nervous system. By increasing vagal tone, our autonomic nervous system is kept in check, shown by an improvement in HRV.
Exercise has also been shown to help people already suffering from cardiovascular concerns. A study of a two-week exercise regime of two 30-minute cycling sessions saw an increased recovery of the parasympathetic nervous system and increased HRV in patients who suffered heart attacks.¹³
Improvements have also been seen in patients with congestive heart failure and type 2 diabetes.¹⁴
Typically, HRV is very low during exercise because our sympathetic nervous systems are almost entirely in control. Our bodies are undergoing rigorous physical activity that requires our organ systems to operate at a much higher capacity.
Directly after exercise, HRV will remain low, and the more intense your workout was, the longer it will take for your HRV to recover to pre-exercise levels.¹⁵ How well your HRV can recover after exercise is an indication of how healthy it is to begin with.
However, not all exercises are created equal. Studies have shown that aerobic training (e.g. cardio, spin, swimming), shows a higher improvement of HRV.
Additionally, higher intensity is correlated with more improvement. A study found that participants who used walking as exercise required more days of exercise per week to obtain the same positive effects on HRV as the participants who used step-aerobics as exercise¹⁶.
Exercise and sleep are both necessary to lead a healthy lifestyle, and with all the benefits they provide for HRV, there really is no reason not to build healthy habits.
So, the next time you decide to workout, pick an exercise that will boost your HRV, and don’t forget to combine that with a good night’s sleep!
Shaffer, F., & Ginsberg, J. P. (2017). An Overview of Heart Rate Variability Metrics and Norms. Frontiers in Public Health, 5, 258. doi.org/10.3389/fpubh.2017.00258.
Michels, N., Clays, E., De Buyzere, M., Vanaelst, B., De Henauw, S., & Sioen, I. (2013). Children’s sleep and autonomic function: low sleep quality has an impact on heart rate variability. Sleep, 36(12), 1939–1946. doi.org/10.5665/sleep.3234.
Goldberger, J. (1999). Sympathovagal balance: how should we measure it? American Journal of Physiology, doi.org/10.1152/ajpheart.1999.276.4.H1273.
Brain Basics: Understanding Sleep. National Institute of Neurological Disorders and Stroke.
Routledge, F. S., Campbell, T. S., McFetridge-Durdle, J. A., & Bacon, S. L. (2010). Improvements in heart rate variability with exercise therapy. The Canadian Journal of Cardiology, 26(6), 303–312. doi.org/10.1016/s0828-282x(10)70395-0.
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. https://doi.org/10.1186/s12938-018-0561-x.
Ferreira, Luana Farinazzo, Rodrigues, Gabriel Dias, & Soares, Pedro Paulo da Silva. (2017). Quantity of Aerobic Exercise Training for the Improvement of Heart Rate Variability in Older Adults. International Journal of Cardiovascular Sciences, 30(2), 157–162. dx.doi.org/10.5935/2359-4802.20170003.