Heart rate variability (HRV) is a useful recovery metric and indicator of athleticism. But what if you’re fit and healthy but have a low HRV? I investigate the factors that could account for this.
The autonomic nervous system regulates the variation in time between successive heartbeats, which is measured as HRV. This represents a key indicator of cardiovascular health that is influenced by a number of factors such as age, physical fitness, and stress levels.
Put simply – a high HRV level indicates a more flexible autonomic nervous system, which is linked to better cardiovascular health and stress resilience. A low HRV, on the other hand, may be an early warning sign of potential health issues such as hypertension, heart disease, or diabetes.
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HRV is a highly individualised measure. Fit and healthy people typically have higher HRV values. But this is not always the case. It is for this reasons that smartwatches typically measure HRV of a person for a few weeks. Once the individual’s baseline is established, their daily HRV values are compared against this range.
So high HRV can be suggestive of increased athleticism. But the link is not definitive.
What if you have a low HRV but are otherwise healthy?
If you are healthy and fit and are seeing low HRV you might be wondering as to the reasons for this. A few different factors that explain low HRV include:
- Overtraining: Athletes who overtrain or do not allow for adequate recovery time may see a decrease in HRV. This is because overtraining can reduce parasympathetic nervous system activity, or the part of the autonomic nervous system that helps regulate bodily functions during rest and relaxation.
- Psychological stress: Emotional stress and anxiety can both lower HRV. This is due to the fact that stress activates the sympathetic nervous system, which is in charge of the “fight or flight” response.
- Medical conditions, such as hypertension, diabetes, or sleep apnea, can also result in a decrease in HRV. Medication used to treat these conditions may have an effect on HRV in some cases.
In addition to these, there is one additional factor which is often overlooked. HRV is also influenced by genetics and some individuals may have a naturally lower HRV.
The author of this article is an example of that. My resting heart rate is typically in the low 50 beats per minute (bpm) and can dip into the high 40s, which is considered an indicator of high fitness. But my HRV rarely climbs above 45-50 milliseconds (ms), which is no better than average for my age.
Medical studies support the notion that genetic factors influence a person’s HRV
An interesting thread has popped up on Twitter citing medical studies looking at the role of genetic factors on HRV. The primary focus is on family history of hypertension (FHH).
One of these is a meta-analysis which evaluates the impact of FHH on blood pressure HRV in young adults (age 18-40). To cut a long story short, results show that FHH negatively impacts BP and/or HRV in young adults.
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Another study looks at middle-aged folks. It found that those with no FHH had higher parasympathetic HRV markers after covariate adjustment versus normotensives with FHH, pre-hypertensives, and hypertensives. Which means altered autonomic function is already present in subjects with FHH.
Yet another study supports the above findings – but with gender differences. It found that amongst young healthy adults men with FHH had lower HRV (along with lower baroreflex sensitivity and ventricular function versus controls). Interestingly, such differences were not found when comparing women with and without FHH. At least not to the same extent.
Work on improving your HRV
The good news is that whatever your current HRV baseline, it is not fixed. Meaning, there are things you can do to improve it.
A recent study published on the National Library of Medicine website goes into details on how to achieve this. The jist of it is that endurance training alone or endurance training in addition to resistance training increases HRV in healthy middle-aged adults. But not resistance training alone. So, the next time you head off to the gym, consider leaving your car in the garage and going for a jog instead.
A few other suggestions include building a consistent circadian rhythm and making sure to put in enough sleep, eating at consistant times and not before you go to bed, making sure to stay properly hydrated and keeping your stress low. Focus on building a consistant HRV baseline and improvements will come in time.
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