Heart rate. It’s one of those things runners either track obsessively or scoff at the mere thought of thinking about it. While I’m not quite obsessed with tracking my heart rate, I do find tracking it very helpful. For me and many others, tracking resting heart rate, if not while running but at the very least first thing in the morning, can reveal a lot about how our training is going or our overall health. If you wake up to a higher than usual heart rate, you know you might be getting sick or need a recovery day. Your heart rate getting lower over time at the same pace? Congratulations, you’re building aerobic fitness!
But as scientists have found in the last few years, your runner’s heart can tell you a lot more than that, if you know how to listen. You might have seen that some of the newer GPS watches will tell you not only your heart rate, but also your heart rate variability, or HRV. Some even purport to tell you how stressed you are based on this information. Apps like ithlete, Sweetbeat, and EliteHRV do the same, claiming to track your recovery and training progress using your HRV.
Should runners track heart rate variability?
Heart Rate Variability Explained.
HRV is the variation in the time between your heart beats as you breathe in and out. If you’re physically or emotionally stressed, your HRV will be lower. If you’re feeling calm and rested, it will be higher. So tracking your HRV can tell you how recovered you are from your last workout; whether you’re getting sick; if you need a day off; and which direction your fitness is heading. Are you becoming more aerobically fit, or are you on the way to overreaching/overtraining? A well-recovered, aerobically fit runner will notice an upward trend in her daily HRV readings as she becomes even fitter. A fatigued, chronically stressed-out runner will see a downward HRV trend over time and eventually reach a state of non-functional overreaching or even overtraining if she doesn’t pay attention to her recovery needs.
So, why the differences in HRV in Ms. Enviably Aerobically Fit vs. Ms. Possibly Overtrained? It’s all about your autonomic nervous system, which controls your internal organs and bodily functions, including your heart rate. The autonomic nervous system has two components: the sympathetic and the parasympathetic nervous systems. The sympathetic nervous system controls the functions you need to take action. Just before you wake, for instance, your heart rate increases, and you secrete the “stress hormone” cortisol (the Cortisol Awakening Response), both of which are partly regulated by the sympathetic nervous system. That “fight or flight” response you get when confronted with an angry ex or the realization you forgot a deadline is also controlled by the sympathetic nervous system.
The parasympathetic nervous system, in contrast, wants you to chill. Save your energy! Lower your heart rate and blood pressure! Digest your lunch, have a nap, forget the ex, meditate.
What this all has to do with HRV: there are parasympathetic and sympathetic nervous system effects on the sinus node of your heart, the group of cells that regulates your heartbeat. High levels of parasympathetic activity affect this node in a way that raises your HRV. Mine is higher on vacation or after a good night’s sleep. High levels of sympathetic activity from life stress or training stress do the opposite. Stressors like poor sleep and a negative worldview send my HRV way down.
So I have to have a good HRV now, too? Great, more pressure!
Yes and no. The point to tracking HRV isn’t to win some prize for most well-adjusted athlete. An upward or downward fluctuation in any given day is expected and normal, influenced by many different factors. And sometimes a low heart rate variability is a sign you’re training right, in the last phase of race training where you’re doing a lot of intensity and aiming to peak soon. This phase of training is meant to produce some fatigue and your HRV may be temporarily lower as your body adapts to the stress. This is a good kind of tiredness known as functional overreaching. The point of the taper is to recover and get even stronger by race day – and you’ll see this recovery reflected in a rebounding of your HRV.
But lots of training with insufficient recovery or training while under prolonged life stress, can eventually lead to bad things: non-functional overreaching and overtraining. I’ve been there. It’s not pretty and it’s surprisingly hard to realize what you’re doing when you’re in the middle of it. If the mood disturbances, fatigue, dead legs, sleep loss and inexplicable weight loss don’t convince you to take a break, maybe seeing a slide in your HRV over several weeks will!
There’s an app for that!
If you have a Bluetooth heat rate strap and a smartphone, you’re just a few clicks away from being able to measure your HRV to your heart’s content.
Sorry. Anyway, there are several HRV apps on the market; I use ithlete. You can use it with a regular Bluetooth heart rate strap or with the specially designed finger sensor. Science says the ithlete finger sensor is as good as a hospital echocardiogram for determining HRV. So every morning, right after waking up, I sit there for one minute breathing deeply with the sensor on my left index finger. At the end of the minute, the app gives a color-coded reading: a number in green means you’re good to go, yellow means take it easy, red means take the day off. This basic reading in the app is based on the change in your HRV from the day before. A drastically lower HRV will be red, a slightly lower HRV will probably be yellow the first day and red if it continues a second day.
You can also track subjective training indicators like training intensity, fatigue, mood, and sleep quality to see which factors affect your overall recovery. Especially useful is the ability to track your HRV over time via the blue line on the graph, which shows the seven-day rolling average. You can see where mine went downhill during the week of April 25th. Whatup, April 29th stomach virus!
The additional, subscription-based ithlete Pro service gives more information, using a statistical technique called z-scoring to plot that day’s reading in relation to the last 30 days on a scatter plot and tell you both how recovered and how “activated” you are. A dot right in the middle of the plot is totally average. High activation, in the top half, can mean high stress levels or oncoming illness, low activation can mean lower energy levels that day. A recent bout of stomach flu sent the red dot almost off the graph in the “low recovery high activation” quadrant… not that I needed an app to tell me not to go running that day.
It’s no good investing in an app and a snazzy HRV-detecting device if you’re not going to do what it says, so I try to take ithlete’s advice even when it chafes. What do you mean I should take it easy? Don’t you know it’s 60 degrees, sunny, and I’m off work? And you don’t want me to run? The app can be eerily accurate, though. Recently I ignored a yellow reading on a Tuesday, only to end up with a bad head cold by Thursday that meant taking it easy for three or four days. As of yet ithlete does not include an “I told you so” feature, but maybe it should.
Is measuring HRV more useful than just taking your resting heart rate every morning? I can only speak for myself, of course, but I never found RHR to be useful. My RHR is pretty consistent unless I’m really sick. And while I believe that there is such a thing as too much data, this isn’t it (for me, anyway). Measuring my HRV every morning has actually made me more mindful of what my body needs to do the things I ask of it. Nothing complicated, just the basics of enough food and sleep, but it’s easy to forget how important those are.
Your HRV sales pitch would be more convincing if you listed some drawbacks.
Ok, you’re right. I can think of a few potential drawbacks off the top of my head, not deal-breakers, but things to be aware of. First of all, an app is no substitute for using your brain. If the app says to go for it, but you know you’re not up to it, go with your gut! And conversely, if the app says take it easy and you had a hard workout planned, do not take 50 consecutive measurements to try and get one that tells you differently. Be honest with yourself: If you see that your heart rate is up and you’re not ideally recovered, do you really need to hammer five miles of intervals that day?
Secondly, don’t mischaracterize the concept of being recovered to think you will or should always feel fantastic. Not every run is going to be great, even if you were the queen of recoveryland that day. C’est la vie. After my experience with non-functional overreaching, though, I find a sense of security in knowing that a bad run doesn’t mean I’m running myself into the ground. It’s just a bad run and my heart rate variability says I’m fine.
So, have I sold you on this concept? Do you already measure HRV? How? And how does it help you in your training?