Heart Rate Variability (HRV): What It Is and How to Improve It
Researchers at Harvard University have gone as far as to say that measuring your Heart Rate Variability is “a visual insight into the most primitive part of your brain” which sounds great but how can us fit folks use it to our advantage?
Brock Armstrong
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Heart Rate Variability (HRV): What It Is and How to Improve It
A few weeks ago, listener Megan wrote to me on Facebook and said: “Hey Brock, would you explain heart rate variability (HRV) in layman’s terms? I’ve heard a lot about it, but don’t quite understand the concept or its use.” I thought that was a great suggestion because HRV is a technique that has been growing in popularity and acceptance in the sport and fitness world. So here you go, Megan: HRV 101.
Most athletes know that getting enough rest after exercise is essential to performance. Still many of us overtrain and feel guilty or lazy when we take a day off. But relentless training can break even the strongest athletes and rest is a necessity to allow your body to repair, rebuild, and strengthen.
Given that it is so difficult for many of us to know when to train hard and when to back off, before we strap on a bluetooth heart rate monitor and fire up our HRV measuring smartphone app, let’s look at some non-HRV ways that we can measure our current state of recovery.
Measuring Workout Recovery
Resting Heart Rate
Sports scientists have confirmed a link between fluctuations in your resting heart rate and overreaching or overtraining. But this link is not easily understood nor directly correlated. Many factors get in the way of it being 100% reliable.
But still, measuring your resting heart rate first thing in the morning is a good place to start. Keeping in mind that day-to-day variations in resting heart rate of approximately five percent are common and are not warning signs. However, increases of greater than five percent are typically a sign of fatigue or overreaching from too much intensity. A decrease of greater than five percent is often observed in cases of too much exercise volume.
Sleep Quality
Having trouble getting to sleep at night, tossing and turning throughout the night, and waking up much earlier or later than usual can all be signs of inadequate recovery.
Sure a restless night can simply mean you didn’t eat enough after a workout, it’s too hot in your room, or you have too much on your mind, but it can also mean that you have depleted the anabolic hormones important for muscle repair and recovery or that you have too much cortisol production. Like resting heart rate, this can be hard to interpret and correlate directly.
Appetite
If you are not getting hungry the way you normally would, it can be a sign that you are under-recovered and need a day or two of recovery.
Your appetite typically decreases with under-recovery, high training load, and fatigue. And this can create a vicious cycle—a cycle that results in consistent negative energy balance and subsequent amino acid, fatty acid, and hormone depletion.
Amount of Muscle Soreness
DOMS (delayed onset muscle soreness) is a completely normal reaction to high training intensity but can increase your risk of injury if followed by insufficient rest and recovery.
Persistent muscle soreness is one sign of overreaching and overtraining. While in some phases of training, you should expect some DOMS, it should not be a chronic condition.
General Energy Levels
We have all experienced those days when we didn’t want to train but ended up having a fantastic workout. We have also all had those days when we didn’t want to train, so we didn’t, and felt much better for it. The trick is to be able to distinguish low motivation from under-recovery and low motivation from non-physical factors, like laziness or being stressed after a tough day at work.
A good way to gauge this is to simply start your workout, get through the warm-up, and then see how you feel. If you’re still tired and dragging-it after the warm-up, you are likely under-recovered and need a day off.
General Mood
In the sports world, POMS (Profile of Mood States) first gained favor among sports psychologists in the late 1970s. Recent research confirms the link between recovery of the mind and recovery of the body, as well as the impact that your mental state can have on recovery. This explains why general apathy, feelings of depression or anxiety, and mood swings often indicate fatigue, impending illness, or under-recovery or overtraining. These markers are also commonly associated with periods of underperformance at your chosen activity or sport.
What Is HRV?
OK, enough beating around the bush. Time to talk about HRV seeing as it is the current reigning champion in the realm of quantifying athletic recovery.
HRV is simply a measure of the variation in time between each heartbeat. This variation is controlled by a part of the nervous system called the autonomic nervous system (ANS). It works regardless of our desire and regulates, among other things, our heart rate, blood pressure, breathing, and digestion.
A healthy heart does not tick along like a metronome. The oscillations and variations of a healthy heart are complex and non-linear. A healthy heart’s beat-to-beat fluctuations are often described as “mathematical chaos.” The variability of what scientists call non-linear systems is said to provide the flexibility our biology needs to rapidly cope with uncertain and changing environments. So, while a healthy biological system exhibits complexity, impaired biology can involve either a loss or an unhealthy increase in complexity.
In an oversimplified nutshell, let’s say your heart rate is 60bpm. With a healthy HRV, each beat is separated by a wide range of milliseconds. With an unhealthy HRV, the beat to beat variability is drastically lower, and a 60bpm heart rate would show an unchanging beat every second. Like a stopwatch versus a jazz drummer.
The healthier your nervous system the faster you are able to switch gears.
The reason for this is that the brain is constantly processing information in a region called the hypothalamus. The hypothalamus, through the ANS, sends signals to the rest of the body to either stimulate or relax different bodily functions. It responds not only to a poor night of sleep or getting yelled at by your boss, but also to the exciting news that you got a raise or to that yummy burrito you ate for lunch.
But, if we have very regular stress, unhealthy diet, poor sleep, dysfunctional relationships, feelings of isolation or solitude, and lack of exercise, this balance may be disrupted and your fight-or-flight response can kick itself up a notch.
As we discussed earlier, the status of your nervous system is an important indicator of your body’s training response. Nervous system measurements can indicate your response to training, and Heart Rate Variability is considered to be a view inside the nervous system.
How Your Heart Works
The origin of your heartbeat is located in what is called a node of your heart. If you are alive, your SA node (sino-atrial) will generate a certain number of electrical impulses per minute, which directly impacts how many times your heart will beat per minute. Easy, right?
Your SA node activity, heart rate, and rhythm are largely under the control of your autonomic nervous system, which is split into two branches, the “rest and digest” parasympathetic nervous system and the “fight and flight” sympathetic nervous system.
When you are well rested and haven’t been training excessively your parasympathetic and your sympathetic nervous system play well together and produce responses in your heart rate variability to respiration, temperature, blood pressure, stress, and more. And as a result, you tend to have consistent and high HRV values.
If you are not well rested, the healthy beat-to-beat variation in your heartbeat begins to diminish and a consistently low HRV value, or HRV values that tend to jump around a lot from day-to-day, indicate an imbalance.
In a strength or speed athlete, or someone who is overdoing things from an intensity standpoint, we often see more sympathetic nervous system overtraining, and a highly variable HRV (a heart rate variability number that bounces around from day to day). With endurance athletes we generally see more parasympathetic nervous system overtraining and a consistently low HRV value. You can read more about that in a study called Decrease in heart rate variability with overtraining.
HRV Frequencies
I hope you are with me so far because we are about to dive deeper. HRV can get even more complex than simply assigning a high or low score.
When you are using a robust HRV tracking tool (like the one from SweetWater Health), you can also track your nervous system’s LF (low frequency) and HF (high frequency) power levels. This is important to keep an eye on for a couple of reasons:
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Having higher power readings from LF and HF can represent a greater flexibility and a robustness in your nervous system.
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More sedentary people have numbers in the low 100’s while fit and active people are often around 900 or higher. The numbers usually grow as fitness and nervous system health improves.
Tracking LF and HF together can truly illustrate the balance in your nervous system. Generally, you want the two scores to be relatively similar. At times when they are not, it may indicate that the body is in a rested state with too much parasympathetic nervous system activity (high HF) or in a stressed state with too much sympathetic nervous system activity (high LF).
What Impacts Heart Rate Variability?
It is commonly agreed upon that as we age, our HRV scores decrease, but there are other factors that can increase or decrease HRV in both the short & long term.
Things that decrease HRV (short-term)
- Stress
- Poor sleep
- Poor diet
- Alcohol consumption
- Illness
- Acute overtraining
- Some medications
Things that decrease HRV (long-term)
- Chronic disease or inflammation
- Chronic stressors or burnout
- Chronic lack of sleep
- Lack of fitness
- Chronic Overtraining
- Unhealthy home or work environment
As you can probably imagine, doing the opposite of that list should result in an increase in your HRV.
The Latest Research on HRV
A new study called Training Prescription Guided by Heart Rate Variability in Cycling revealed some very promising results.
Seventeen well-trained cyclists were recruited, with an average age of 39 and riding experience of 13 years, and had their cycling performance measured three times over the period of the study:
- At the beginning
- After 4 weeks of baseline training
- After 8 weeks of guided training
After that, the group was split into HRV-guided training program and a traditional (intuitive) training program for eight weeks.
The major finding of this new study was that HRV-guided training led to significantly greater increases in peak power (five percent), power at Ventilatory Threshold 2 (14 percent), and power over the 40-minute time trial (seven percent) compared to traditional training.
When looking at the participant’s performance on the 40 minute Time Trial, it is clear that the HRV-guided training produced many of the best results while also avoiding the worst outcomes.
HRV Tips
If you decide to start tracking your own HRV for training or general health, here are some tips.
1. Higher is not always better.
If your score is always high, it can actually be a sign that you aren’t pushing yourself hard enough. Remember that fitness is built through stress and rest so sometimes seeing some lower scores is exactly what we are after. Just don’t let them stay too low for too long.
2. Consistency is key.
Good measurement practice will increase the reliability of the test and produce better results. So, make sure to take the measurement first thing after waking (avoiding the effects of caffeine, food, and any external stress), use the same body position every day (don’t lay down one day and sit up the next), and don’t manipulate your breathing rate (inhaling increases your heart rate while holding your breath and exhaling slow it down).
3. Don’t compare your numbers to others.
Just like race times, run streaks, VO2 Max, and anything else people can brag about on social media, you may see people posting their HRV scores on there as well. Don’t fall into this trap. Establish your own baseline and keep an eye on your own trend. This isn’t a competition—no one gets a medal for having the highest HRV score.
4. Trend trumps accuracy.
No matter which system you choose to measure your HRV with (and there are many to choose from), don’t get hung up on the accuracy. Just like a home scale, an activity tracker, or a step counter, the important part is whether or not your trend is moving in the desired direction. The actual accuracy of the value or score is less important, in the grand scheme of things.
5. Interpret the values.
Every morning that you are training, I suggest that you check in on your HRV. Then, based on your HRV score, judged against how you feel, your anticipated recovery state, or where you are in a training block, see whether or not your score matches what you expect it to be or what you want it to be. If it doesn’t line up (for example, you are in a recovery period but your HRV is still lower than usual) you can adjust your workout for that day. If it lines up well with what you expect or desire to see, you can carry on with training as usual.
Should You Monitor Your HRV?
HRV is an interesting and noninvasive way to peek at potential nervous system imbalances. If an athlete is in more of a fight-or-flight mode, the variation between subsequent heartbeats is low. If that same athlete is in a relaxed state, the variation between beats is high. In other words, the healthier your nervous system the faster you are able to switch gears, which contributes to more mental flexibility and overall physical resilience.
Even if you aren’t worried about your training or recovery, research has shown a relationship between low HRV and states like depression or anxiety. A low HRV has even been associated with an increased risk of death and cardiovascular disease. People who have a high HRV may have greater cardiovascular fitness and show more resilience to stress.
Even more interesting, HRV may provide personal feedback about your lifestyle and help to motivate those folks who are considering taking steps toward a healthier and fitter life.
So, if you decide to track your own, watch how your HRV changes as you do things like becoming more mindful, experimenting with meditation, increasing your sleep duration or quality, and especially increasing physical activity in your life. This can be a nice way to track how your nervous system is reacting not only to your athletic training, but also to your emotions, thoughts, and feelings.
For more heartfelt info, variability tips, and to join the beat conversation, head over to Facebook.com/GetFitGuy or twitter.com/getfitguy. Also don’t forget to subscribe to the Get-Fit Guy podcast on Apple Podcasts, Stitcher, Spotify, Google Play or via RSSopens XML file .
About the Author
Brock Armstrong was the host of the Get-Fit Guy podcast between 2017 and 2021. He is a certified AFLCA Group Fitness Leader with a designation in Portable Equipment, NCCP and CAC Triathlon Coach, and a TnT certified run coach. He is also on the board of advisors for the Primal Health Coach Institute and a guest faculty member of the Human Potential Institute.