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6 Low HRV Symptoms (And What Causes Them)

HRV, or heart rate variability, is a measure of the time between heartbeats. HRV measures vary by person and over time, fluctuating based on lifestyle choices and lived experiences, from stress levels to sleep patterns, exercise habits, and levels of physical exertion the body, day-to-day. 

Unlike for a heart rate or blood pressure measurement, there is no determined “ideal” HRV rate. And while HRV values vary greatly per person, and by day and circumstance, a higher HRV is considered a better health indicator than lower HRV, overall. 

More notably, a lower HRV has been linked to numerous markers for less-than-optimal health, wellbeing and functioning, which is why paying attention to your HRV measurements and tracking these data trends over time, with the help of WHOOP, can help you perform and feel better, and work more effectively and efficiently towards your overall health goals.

Paying attention to changes in your HRV trends over time is also a way to track the success of lifestyle interventions like fitness routine or dietary changes. A rise in HRV shows that your efforts are paying off, while a drop in HRV could indicate that further adjustments need to be made.

HRV is a crucial cardio health indicator that can be monitored to unlock insight into health and that can be easily monitored at home with a convenient fitness wearable like WHOOP. Discover what HRV is and what a low HRV measure can suggest.

What is HRV?

HRV, or heart rate variability, is a measure of the time between heartbeats. The time between each beat varies, and therefore, there could be 0.7 seconds between two beats and 1.20 seconds between two other beats, as an example. These individual measures of the time between two heartbeats are known as RR intervals, and are recorded in milliseconds.

HRV is an indicator of the function of the body’s autonomic nervous system (ANS), which controls key involuntary processes like heartbeat, blood pressure, and breathing rate. The ANS comprises two opposing branches, the sympathetic and parasympathetic nervous systems. 

In response to stress or other perceived threats to safety or well-being, the sympathetic nervous system activates the body’s “fight or flight” response. This ANS branch prepares the body to take action to get out of a threatening situation, resulting in an increased heart and respiration rate to supply the body with more oxygen, and increased pupil size to improve vision. The body also limits digestion and stimulates glucose to be made to boost energy levels.  

The parasympathetic branch is responsible for the “rest and digest” response, which is activated during periods of relaxation and directs the body to perform processes key to survival. The parasympathetic branch decreases heart rate, lowers blood pressure and respiration rate, and kick starts digestion. 

HRV is a measure of the interaction and balance between the two ANS branches. When the two branches are functioning optimally, they will both be sending opposing directives to the heart — the parasympathetic system tells the heart to beat slower, while the sympathetic system tells the heart to beat faster. 

This interaction is a sign of a balanced nervous system, and results in the fluctuations in the time between heart beats that can be picked up and measured as HRV.

What is An Ideal HRV?

While other physiological measures like heart rate and blood pressure have ranges that are considered ideal for the average person, HRV is a much more individualized metric. There is no standard HRV range. 

That being said, a higher HRV is considered to be an indicator of better fitness and resilience to stress. A high HRV means that the body is actively responding to both branches of the ANS, indicating that the body is responsive to feedback and primed to perform optimally. 

It’s important to note that HRV is a very sensitive metric. HRV readings can fluctuate from morning to night and from one day to another. Readings from two different people can also be very different when compared. 

Certain factors have been linked to specific trends in HRV readings. For example, older individuals tend to have a lower HRV, while women usually have a lower HRV than men, and elite athletes typically have higher HRVs than non-athletes. 

When monitoring your own HRV, it’s much more informative to track trends in your HRV than to compare your readings to other individuals. Focusing on your HRV is the best way to get insight into what is typical for your body and how ready you are to perform to the best of your abilities at any given time. 

6 Symptoms of Low HRV

A higher HRV is associated with a balanced nervous system and better overall fitness. A lower HRV, on the other hand, is considered to be a sign that the body may not be functioning optimally. With low HRV, there is an imbalance in the body’s response to the two branches of the ANS. One of the branches is dominant, signaling more strongly to the heart than the other. 

This most commonly occurs when the sympathetic nervous system is the dominant branch. In the short run, this isn’t a problem. During intense physical activity, for example, the sympathetic branch activates to meet the demands placed on the body. 

However, a low HRV outside of physical activity is not considered ideal. It’s a sign that the sympathetic nervous system is in overdrive and is depleting the body’s resources due to things like illness, stress, fatigue, overtraining, or dehydration. This makes it more difficult for the body to perform at its best. 

Staying on top of your HRV readings and monitoring your HRV trends over time allows you to recognize dips in HRV and take action.

These are a few common symptoms of low HRV to be aware of:

  • Fatigue — Individuals with low HRV tend to report higher scores of fatigue. It’s also common for those with low HRV to experience chronic fatigue. Healthcare providers and patients can monitor HRV trends to manage conditions such as chronic fatigue syndrome.
  • Inflammation — A meta-analysis of studies on the relationship between HRV and inflammation found that HRV can be used as a marker of inflammation in the body. Lower HRV was associated with more inflammation. Research has also linked elevated CRP levels, a well-known inflammation marker, to lower HRV.
  • Autonomic Dysfunction — Autonomic dysfunction, also called dysautonomia, occurs when the proper function of the ANS is disrupted. It can harm the ability of many other bodily systems to operate normally. Autonomic dysfunction can make regulating heart rate, blood pressure, body temperature, and sweating difficult. Low HRV occurs when one branch of the ANS is dominant, which is one example of autonomic dysfunction.
  • Poor Sleep — Reduced sleep quality can be an indicator of low HRV. Research has found that sleep deprivation leads to a decline in HRV, demonstrating a negative relationship between sleep disruptions and HRV.
  • Anxiety and Depression — Low HRV has also been linked to higher self-reported scores of anxiety and depression. Research has found that individuals who experience more severe symptoms of major depression tend to have lower HRV and that HRV may be able to be used as a marker for depression severity. Additional research has linked anxiety disorders, including PTSD, generalized anxiety disorder, and panic disorders to low HRV.
  • Reduced Cognitive Function — Another symptom of low HRV is difficulty completing everyday cognitive tasks. One study found that individuals scoring poorly on inductive reasoning tasks were likelier to have low HRV. Further research has found that low HRV is linked to impaired learning and memory through verbal recall and reduced executive function.

A temporary low HRV reading is not a cause for concern. Several factors can cause brief declines in HRV. If you run a marathon, your sympathetic nervous system kicks into high gear to supply your body with the oxygen and energy it needs to perform at a high level. External factors like heat exposure, loud noises, and pain can also increase sympathetic nervous system activity. 

In all of these cases, the dominance of the sympathetic nervous system would be expected to be temporary, leading to a temporary decline in HRV. It’s only when HRV readings are consistently low over time, outside of physical activity or environmental changes like an increase in temperature or noise level, that they can cause unpleasant symptoms and hurt wellbeing. 

How to Improve HRV

Low HRV and the symptoms that it causes can significantly disrupt everyday life. Fortunately, there are lifestyle adjustments you can make to help improve HRV and restore balance to the function of your autonomic nervous system.

These are some strategies to try to increase HRV:

  • Exercise — One of the best ways to increase HRV is by following a consistent fitness regimen. Research has found that regular exercise can lead to improvements in HRV. Specifically, studies show that workouts in Zones 2 and 3 improves overall performance and health. 
  • Proper Diet — A healthy diet is associated with high HRV. Specific foods have also been found to increase HRV, including fish, nuts, yogurt, and foods rich in vitamin B12. Maintaining a routine meal schedule is also important for overall health and HRV. Try to eat at the same times each day and avoid eating close to bedtime.
  • Manage Stress — Stress can negatively impact HRV, so it’s important to take measures to reduce your stress level. Stress-relief strategies include connecting with loved ones, listening to music, reducing caffeine intake, and activities like yoga, gardening, drawing, or painting. 
  • Breathing Exercises — Breathing exercises can help you manage your stress and improve HRV. Research has found that breath control techniques can improve HRV and autonomic nervous system function. WHOOP in-app breathing exercises can support you in your efforts to improve your HRV via this simple, relaxing yet highly effective strategy.
  • Get Enough Sleep — Boosting your sleep hygiene is an excellent way to improve HRV. Keeping sleep and wake times consistent helps you get enough sleep each night, maintains the body’s circadian rhythm, and increases time spent in REM and deep sleep.
  • Light Exposure — Exposure to natural sunlight is another way to promote the body’s natural circadian rhythm and improve HRV. As little as 20 minutes of light exposure each morning after waking can significantly impact energy levels, hormone production, and sleep consistency.
  • Cold Thermogenesis — Exposing the body to cold temperatures can also be a useful strategy for increasing HRV. Brief exposures to the cold through ice baths, cold showers, or plunges stimulate the vagus nerve, leading to parasympathetic nervous system activation and improvements in HRV.
  • Intermittent Fasting—Also referred to as time restricted eating, intermittent fasting refers to the practice of limiting the times of the day during which food is consumed to occur between a 6 to 10 hour window, in your waking hours, and thereby prolonging the hours between your last meal of the day and your first meal of the next day, without restricting calorie intake or changing diet, necessarily. This simple mealtime shift has also been shown to improve HRV when done correctly. 

Track HRV with WHOOP

HRV is such a sensitive and variable physiological metric. WHOOP calculates HRV when you are in your deepest period of sleep each night to establish a reliable baseline HRV. WHOOP uses this nightly HRV score to generate your daily Recovery Score, which lets you know how ready your body is to perform and take on the day. 

Rely on WHOOP for insightful, accurate HRV tracking.