Health tracking gadgets are looking at a new metric for evaluating fitness: heart rate variability, or HRV.
Manufacturers of tracking equipment claim that your HRV can reveal whether you’re getting quality sleep, overtraining, drinking too much alcohol, or even if you’re experiencing too much stress in your daily life.
So, are they worth the hype?
How to measure heart rate variability
Heart rate variability, or HRV, is a measurement of the variance between heartbeats. The period of time between each beat is called an RR interval.
This variance between RR intervals can be explained by your autonomic nervous system, which controls many involuntary functions of your physiology that maintain homeostasis, including regulating temperature, salt concentration, and blood sugar levels.
It also controls physical reactions to emotions.
For example, when you’re excited or nervous, your autonomic nervous system increases blood pressure and heart rate, among other responses. As you might have guessed, your nervous system also controls your heartbeat.
(Image source: Young, et al.)
The autonomic nervous system (ANS) is separated into two branches: parasympathetic and sympathetic.
- The parasympathetic division handles “rest and digest” functions, like digestion. With respect to heart rate, it can be thought of as a deactivating response, as it decreases heart rate.
- The sympathetic division is often called a “flight or flight” response. It prepares the body for an output of energy, which usually involves an increase in blood pressure, pupil dilation, increased glucose production, and increased heart rate.
From moment to moment, your ANS sends signals to your parasympathetic and sympathetic nervous systems to stimulate or relax various functions. Which response is activated depends on stimuli from the environment.
For example, bad sleep, an emotional conversation, spicy food, or multiple hard days of training can affect how your ANS responds.
Now, as you’re reading this, find your pulse. Notice a variation between beats? It’s completely normal and is the result of your parasympathetic and sympathetic nervous systems simultaneously sending signals to your heart.
What’s a good HRV?
A high HRV is usually considered a sign of health.
That’s because activation of your sympathetic nervous system (“fight or flight”) usually increases stress and decreases HRV, while activation of your parasympathetic nervous system does the opposite.
As one researcher put it, HRV “reflects autonomic dysregulation.”
While this may sound a bit reductive or simplistic, research does suggest that generally speaking, a high HRV suggests better overall health. (Kemp, et al.)
What does my HRV say about my health?
HRV depends on a host of factors, including age, gender, genetics, diet and nutrition, alcohol consumption, sleep quality and quantity, stress, and training habits.
As you can see, age is one of many factors that contribute to your HRV. When considering whether you have a “good” HRV or not, it’s important to pay attention to how your HRV changes over time, rather than what it reads on any given day.
(Source: Whoop, a HRV monitor manufacturer)
Psychological health and HRV
In a review of the relationship between HRV and mood, anxiety, and alcohol dependence, researchers found that HRV was a psychophysiological marker of mental and physical wellbeing.
They saw that those with mental distress had on average a lower HRV than control groups. Further, researchers claim that HRV may relate to how motivated someone is to engage socially, self-regulate, and handle stress. (Kemp, et al.) (Kim, et al.)
One analysis over a 10-year period studied the relationship between HRV and depression. The number of participants ranged from 2,334 to 2276.
Two sets of data were taken, one between 1997-1999 and the second from 2007-2009. Researchers found that depressive symptoms were inversely related to HRV, meaning the more severe the depression, the lower the participant’s HRV.
They also found that lower baseline HRV was associated with a lower likelihood of depression during the follow up study. This finding was only consistent for men. (Jandackova, VK, et al.)
Disease and HRV
There is evidence that HRV is a biomarker for a range of diseases, including diabetes and cardiovascular disease.
One study looked at the relationship between HRV and carotid artery atherosclerotic plaque in patients with type 2 diabetes. They monitored the HRV of 61 diabetic patients, with studies being carried out 5-6 years after diagnosis and repeated 8 years after diagnosis.
They found that HRV is associated with “the extent and progression of carotid atherosclerosis in type 2 diabetes.” (Gottsater, et al.)
HRV and diet
HRV is associated with the food we eat.
As Young, et al. points out, a high HRV is related to a Mediterranean diet, fish consumption, multivitamins, and losing weight, while a diet high in trans-fat is associated with a low HRV. (Mozaffarian et al.) (Soares-Miranda et al.) (Pomportes et al.) (Zulfiqar et al.)
While it may not be surprising that a low HRV corresponds to healthy eating, it may surprise you to learn that there is research that suggests mutual causation.
A poor diet may cause a low HRV, and a low HRV may cause a poor diet. (Young, et al.)
What does HRV say about athletes?
HRV monitor manufacturers claim that you can use their products to aid training.
Limited research supports this claim.
One study looked at 26 healthy, moderately fit males randomized into three groups: predefined training group (TRA, n=8), HRV-guided training group (HRV, n = 9), and control group (n = 9).
- The four-week training period consisted of running for 40 min at either a low or high intensity.
- The TRA group trained 6 days a week, with two sessions at low and four at high intensity.
- The training program for the HRV group was based on individualized data based on HRV.
- An increase or no change in HRV resulted in a high-intensity run, while a decrease in HRV resulted in either low-intensity training or a rest day.
- Before and after the four week training period, VO2 peak and maximal running velocity were tested.
- Researchers found no significant differences in VO2 peak but did see an increase in running velocity, concluding that cardiorespiratory fitness can be improved by monitoring HRV. (Kiviniemi, et al)
How to improve heart rate variability
According to Whoop, a leading manufacturer of wearable HRV devices, HRV can be improved by:
Intelligent Training. Don’t overdo it and push too hard for too many days without giving your body an opportunity to recover (see below).
Hydration. The better hydrated you are, the easier it is for your blood to circulate and deliver oxygen and nutrients to your body. Aiming to drink close to one ounce of water per pound of body weight each day is a good goal.
Avoid Alcohol. One night of drinking may negatively affect your HRV for up to five days.
Steady Healthy Diet. Poor nutrition has adverse effects on HRV, as does eating at unexpected times.
Quality Sleep. It’s not just the amount of sleep you get that matters, but also the quality and consistency of your sleep. Going to bed and waking up at similar times each day is beneficial.
Auto-Regulation. In general, trying to get your body on a consistent schedule (in particular with sleep and eating) is helpful. Your body does things more efficiently when it knows what’s coming.
What devices measure HRV?
The following devices can help you measure and track HRV:
Final thoughts on heart rate variability
There is a clear link between a high HRV and general health. HRV is a biomarker that is associated with depression and anxiety, as well as diabetes, cardiovascular disease, and morbidity.
HRV can function as an indicator of a healthy diet.
For athletes, HRV can be used to determine when to train hard and when to back off.
Tracking HRV might be a great way to prompt users to change their behavior. Being able to track the way diet, exercise, sleep, and stress all impact overall fitness is a powerful motivator.
That being said, tracking any marker of fitness can be positive, and tracking doesn’t have to be expensive.
- For example, writing down what you eat during the day can lead to healthier food and beverage choices throughout the day.
- Body composition can be monitored by measuring the circumference of legs and arms.
- Further, overtraining can usually be diagnosed with a decrease in performance and an increase in fatigue.
- All of these methods are free and effective.
But, if gathering this kind of data interests you and you can afford the gadgets necessary, then there is no reason not to track your HRV.
However, keep in mind that at this date, there hasn’t been enough comparison data on commercially available HRV monitors to know which are most accurate.
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