Common Scenarios with Heart Rate Variability (HRV)

When your HRV goes up, it does not mean you should feel great and ready to tackle the world, and when your HRV goes down, it does not always mean that you need to bubblewrap yourself and lay off exercise. If you expect your HRV to act a certain way and it does the opposite, don’t worry, you’re not broken, but figuring out the meaning behind your unexpected HRV may require a lot of thought.

To best prepare ourselves in answering the why behind your HRV, let’s recap on the physiology of HRV.

The Science and Sense of HRV

From reading ‘What is HRV’, we know that HRV is the variation of time between consecutive beats, and this variation is regulated by our Autonomic Nervous system.

Our Autonomic Nervous system is made of 2 components:

Sympathetic Nervous System
'Fight or Flight’

Parasympathetic Nervous System
’Rest and Digest’

Typically, when the Parasympathetic System is dominant, we see more variation between heart beats, which means HRV goes up. When the Sympathetic System is dominant, we see less variation between heart beats, which means HRV goes down. These relationships make HRV a good proxy to see how our autonomic nervous system is holding up, which, with proper context, correlates to how our body is coping with our daily stressors.

But why should you care?

Regulating your autonomic nervous system has been repeatedly proven to improve your well-being, amplify your performance, and enhance your mental health - to name a few benefits. A poorly regulated autonomic nervous system, which is indicated by a chronically low HRV (relative to accepted population norms) is correlated with poor cardiovascular health, predisposition to stress.

‘I know I’m stressed and not sleeping well - Why do I need HRV to tell me the obvious?’

Our HRV doesn't just correlate to the stressors we subjectively feel. This phenomenon was well demonstrated during the height of the COVID pandemic, where people noticed a suppressed HRV, in the absence of any other obvious stressor, before experiencing any symptoms.

This demonstrates that changes in our autonomic nervous system can happen without us feeling any different, and although it’s not always going to indicate that you’ve contracted the plague, it is enough of a reason to check in with yourself and reflect on what is happening with you.

With that knowledge, let’s see if we can explain some common scenarios with HRV. All these scenarios assume that the device you use takes measurements that are accurate and a true representation of your HRV. These scenarios are based on population values, and your HRV may act differently, and if they do - feel free to contact us and we’ll try our best to give you the answers.

I exercised yesterday and my HRV has gone down

When you exercise and your HRV goes down, this usually indicates that your body is recovering from the stressors of your exercise.

Why does it respond this way?

A combination of a decrease in Parasympathetic activity (rest and digest) and an increase in sympathetic activity (’fight or flight’) causes the drop in HRV.

Your device may suggest your HRV is in the red and tell you to ‘go easy’, but the reality is - how you feel is the dealbreaker, and when it comes to making decisions about what you want to do for the day - that decision is yours.

I exercised yesterday and my HRV has gone up

It’s important to know that your HRV is not solely influenced by exercise, so even if you exercised hard, you may have gotten more restful sleep, abstained from alcohol for the night, or a litany of different things that could contribute to your increased HRV.

However, if you’re fairly confident that no other factors would greatly contribute to an increased HRV, and your exercise/life circumstances recently have been demanding, you may be in a state of functional overreaching.

Functional overreaching is hypothesised when an increase in HRV is seen in the setting of an increased training load. The mechanism is not fully understood, but, most likely, it arises from hyperactivity of the Parasympathetic Nervous system, which is not withdrawn despite heavy exercise. A blunting of your maximal heart rate during exercise further supports the fact that you are in a state of functional overreaching, as you limit the ability of the sympathetic nervous system to fully influence your heart pacing. Functional overreaching is relatively rare, but it is a fantastic example of how increase in HRV does not mean you should feel great.

I exercised hard and my HRV is the same

You gave it your all, so naturally you expect your HRV should go down. However, you wake up only to see your HRV is in and around the same as it was for the last 7 days. Why? There are many reasons.

The most important concept to understand in this scenario is that HRV is not reflective of how hard you exercise, how much stress you’re under, or how sick you may be. HRV is a proxy into how your body manages these stressors. So a ‘normal’ HRV after intense cardiovascular exercise is suggestive that your body can cope with the stress of the load.

We say cardiovascular exercise because 'strength/weight' training is poorly correlated with your Autonomic Nervous system, and, thus, HRV does not usually see a sizeable shift post strength workouts. That’s not to say you will never see an impact on your HRV from anaerobic exercise, but there will be a mismatch between how you subjectively feel, with muscle soreness and stiffness, and your HRV.

I feel stressed and my HRV is going down

If you’re feeling stressed, chances are your ‘fight or flight’ nervous system is engaged, and your HRV is expectedly impacted by this. There is no dose-effect relationship, so don’t expect your HRV to plummet the night before a big exam, or if you’re experiencing more stress than usual.

HRV is hypothesised as being a good measure to see if you’re objectively stressed, but bear in mind, HRV considers all stressors, and not just your stressor of interest, so application of this outside of lab settings is difficult.

If you are feeling temporarily stressed, controlled breathing, mindfulness, and, if applicable, therapy can help to negate the effects of stress.

Nothing in my life has changed and my HRV is greatly reduced

A suddenly reduced HRV in the absence of any obvious stressor is enough to get us reflecting on exactly whats been happening lately. Assuming the measurement is accurate, we can assume that our body is dealing with a stressor that we’re not subjectively aware of. This stressor isn’t just limited to your exercise, mental health, hydration status etc, but it also includes the possibility of the stressor being an illness.

The COVID pandemic illustrated this phenomenon well, with a decrease in HRV predating the symptoms and/or diagnosis of the illness by as much as 2 days.

As interesting as this phenomenon, HRV is a sensitive tool, but far from specific. Given the plethora of stressors that can cause a reduced HRV, the take home message in this scenario is pay attention to your self, and if you’re suspicious of a viral illness, take necessary precautions.

I have a chronic illness and my HRV is going down

If you live with a chronic illness that frequently flares, e.g. IBD, Rheumatoid Arthritis, Asthma, you may have noticed changes in your HRV prior to, or during, a flare. This is definitely not always the case for all individuals living with an illness, and even effects on HRV is variable within individuals, but for some, HRV can give good insight into how you are responding to certain events/interventions, e.g. new therapy, withdrawal of current therapy, lifestyle change.

However, this area is painfully lacking in any substantial, convincing evidence, and so in this situation, it is an entirely personal experience. Using Cambrean to aggregate and compare your data before and after intervention can indicate whether this is a good bio-marker to track your pathway.

I have a low HRV and a low resting heart rate (<45 bpm)

If you have a particularly low resting heart rate, for example a heart rate that is consistently below 45 bpm, your vagal nerve, which expresses the Parasympathetic Nervous system, is so dominant that it saturates your hearts natural pacemaker. This saturation is far from a bad thing, but it does interfere with the variability of your heart beats.

Remember that in previous situations, although one system would have a dominant impact on your body, it would not eradicate the effects of the opposing system e.g when you’re stressed and the sympathetic nervous system is dominant, it does not mean the parasympathetic nervous system is absent.

However, in this case where you have a particularly high vagal tone, the impact of the sympathetic nervous system on your heart rate is greatly impeded, which, in turn, lowers the variability between your heart beats even-though your parasympathetic nervous system is dominant. As a result, your HRV will appear reduced.

Once you’re awake and reacquainted to a world full of stressors, the parasympathetic nervous system will lose its dominance , and your HRV will paradoxically increase. This is good news for people who take their HRV reading in the seated position, or manually after a set routine, but unfortunately, this is not so informative for overnight, automatic measurements in users with a low resting HR.

My HRV is always low, but I do all the right things

You eat well, you train well, you meditate, you abstain from alcohol, don’t smoke, and still your HRV is relatively low compared to peers.

Whenever I speak to users about this circumstance, my first thought is ‘are they over-training? , under-eating, or stressed?’ How much is this user listening to their body’s cues, or performing introspection?’ More often than not, it is an issue of circumstance and lifestyle.

However, if this scenario is applicable to you, and you are certain that no unaccounted stressor is at play, then remind yourself of what constitutes your HRV baseline, which we cover here. Your baseline is heavily influenced by your genetics and this may be the explanation for your low baseline.

If despite changing your lifestyle, your baseline does not change, then genetics may be the answer, but we urge you to address your lifestyle, perform introspection, and out-rule any underlying cause before pinning this up to genetics.

Bottom Line

The cases above are intended to help you in understanding yourself, however, they are intended as a general rule of thumb, and not a catch-all answer to certain situations. The theme of all the above scenarios is that, without context, the numbers are meaningless.

You can also follow Marco Altini (founder of HRV4Training) and Andrew Flatt who are pioneers in the world of HRV.

References

1. Heart rate variability from short electrocardiographic recordings predicts mortality from all causes in middle-aged and elderly men: The Zutphen Study https://pubmed.ncbi.nlm.nih.gov/9149661/
2. Reduced heart rate variability and mortality risk in an elderly cohort. The Framingham Heart Study
https://pubmed.ncbi.nlm.nih.gov/8044959/
3. Biofeedback of Heart Rate Variability and Related Physiology: A Critical Review https://link.springer.com/article/10.1007/s10484-010-9133-y
4. Chapter 5 - Sympathetic and parasympathetic systems in meditation https://www.sciencedirect.com/science/article/pii/B978012818266600006
5. Contextualizing Parasympathetic Hyperactivity in Functionally Overreached Athletes With Perceptions of Training Tolerance
https://pubmed.ncbi.nlm.nih.gov/26640275/
6. Autonomic neural control of heart rate during dynamic exercise: revisited https://physoc.onlinelibrary.wiley.com/doi/full/10.1113/jphysiol.2014.271858
7. Stress and Heart Rate Variability: A Meta-Analysis and Review of the Literature https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5900369/
8. Heart rate variability in health and disease
https://pubmed.ncbi.nlm.nih.gov/7618063/
9. Heart rate variability in critical illness and critical care
https://journals.lww.com/co-criticalcare/Abstract/2002/08000/Heart_rate_variability_in_critical_illness_and.7.aspx