Whether you’re a professional athlete or a weekend warrior, taking a break from mental work to hit the gym at weekends, recovery is an important part of how you train.
When we don’t recover sufficiently we end up decreasing our performance and health rather than getting the results we desire – higher performance, beating our records and increasing our health and wellbeing overall. In today’s chronically stressed world, it’s all too easy to over train as we are so used to the constant stress burden.
Most people are aware of this now. But it’s still difficult to manage, even with this knowledge. How do we know when we need to take a break from training? When a workout is going to have an overall negative impact rather than the positive one we seek?
Enter “Heart Rate Variability” also known as HRV.
HRV is being increasingly used by professional athletes and the everyday gym goer to attempt to better manage recovery by providing an estimate of when we are over stressed vs. well recovered. Trying to answer the question – should I leave it a few more days before my next workout? Or should I go easy in today’s workout?
Over the last few years a large number of devices and applications have been hitting the market so HRV is a lot more accessible now. With just an iPhone or Android app and a relatively cheap sensor you’re ready to go. While many of these HRV apps look very straightforward, there is actually a lot to them with different metrics, and correct vs. incorrect approaches to using them.
To cover the HRV topic in depth, today’s guest is Andrew Flatt, owner of the blog HRVTraining.com – which is one of the best resources on using HRV for training I’ve found to date.
Andrew is a PhD student at the university of Alabama who has been working in the Human Performance Lab at Auburn University on research related to HRV and exercise. He has been making use of HRV since 2011 to monitor and optimize his own training and that of the athletes he coaches. He is also an accomplished athlete himself, and was the 2010 Canadian National raw powerlifting champion.
Andrew is very hands on and has done a lot of on the ground work with HRV, so he has a great practical as well as research-based perspective on how to use heart rate variability to optimize training.
- What HRV (Heart Rate Variability) is and what it measures
- How to use HRV to optimize your workout schedule, cycling of workouts and recovery from illness
- The mechanisms behind HRV: vagal tone, autonomic nervous system activation, sympathetic and parasympathetic activity
- A review of the different HRV metrics, and why RMSSD is recommended for convenience and non-professional use
- The devices and apps you need to track your HRV at home and their accuracy (EKG/ ECG, finger light sensor, ear light sensor, phone and web apps)
- Additional features that are useful in the apps to give more meaning to the HRV data
- The impact of lifestyle activities on HRV (partying, sleep, sickness, alcohol and diet)
- Benchmarks of HRV scores for strength and cardiovascular athletes vs. non-athletes – what’s a good HRV that indicates good recovery? What’s a bad HRV that indicates a need to recover?
- Taking your readings methodology – arguments for Supine (lying down) vs. standing up
- How and when to take your HRV readings to ensure that the data is accurate and meaningful for optimizing training
- How HRV varies according to your age, gender, lifestyle, training schedule and type of training (cardiovascular vs. strength/ resistance training)
- What Andrew sees coming up over the next years in the HRV domain and how it’s going to be useful
- Andrew’s top recommendations on using data to improve decisions around training and health
Biomarkers in this Episode
- Heart Rate Variability (HRV): Measures how your heart rate varies over time. Research studies link HRV to recovery status, stress and other aspects of human physiology.
- R-R intervals: Time interval in between heart beats (R = peak of heart beat).
- Resting Heart Rate (RHR): Measure of your heart rate at rest (typically measured upon waking).
- RMSSD (Root Mean Square of the Successive Differences): A measure used to calculate HRV that has proven to be reliable and is used in a lot of the research studies – Andrew’s preferred measure.
- lnRMSSDx20 (RMSSD with natural log and multiple of 20 applied): Applications have begun using this measure, which is basically RMSSD scaled to an index of 100, to make it more user friendly.
- LF (Low Frequency): Spectral measure that indicates combination of parasympathetic and sympathetic activation.
- HF (High Frequency): Spectral measure that indicates parasympathetic activation.
- Coefficient of Variation (CV): Measure of variance across a set time period (Andrew has found to have good correlation vs. weekly mean value).
- 7-Day Trailing Average HRV: Average of HRV values used to track your progress over time. Andrew uses this mostly to guide his training now.
Devices/ Apps from the Episode
HRV for Training
- HRV4Training: Has a choice between 60 second, 2 minute and 3 minute data collection duration.
- ithlete: Combined sensor and monitoring app using a short measurement duration of 50 seconds. Andrew has used this since 2011, and mentioned using their Finger Pulse heart rate sensor.
- SweetWater Health and SweetBeat: Sweetbeat is a HRV application that works with a variety of sensors like the Polar chest straps.
- Bioforce HRV
- Tinké: A complete solution for HRV embedded within a device.
- Polar H7 Heart Rate Sensor: Works with HRV apps using the Bluetooth smart technology.
- HeartMath Inner Balance for iOS or emwave2: Damien mentioned use of the ear sensor technology with these devices (Note: HeartMath devices are not designed for use with training optimization).
Other HRV Devices
Other Resources Mentioned in this Episode
- HRVTraining.com: Andrew regularly blogs about the studies he’s working on and ongoing insights he pulls together on HRV for training.
- Andrew’s Twitter: @andrew_flatt
- International Journal of Sports Physiology and Performance
- European Journal of Applied Physiology
- European Journal of Sports Science
- Journal of Sports Sciences
- The Journal of Strength and Conditioning Research
- Martin Buchheit
- Daniel Plews (Twitter @theplews1)
- Jamie Stanley
- Fábio Yuzo Nakamura (Twitter @Fabio_UEL)
- Joel Jamieson (Twitter @JoelJamieson) (8weeksout.com, bioforce)
Journals Covering HRV Research
Researchers and People to Follow for More HRV Info
[Andrew Flatt]: The pleasure is mine, Damien. Thanks for having me.
[Damien Blenkinsopp]: Thanks. What I thought we would do to start with is jump into what is HRV a little bit – Heart Rate Variability – so that people who haven’t come across this before can have a rough understanding of what it is and where it was.
[Andrew Flatt]: Sure. So heart rate variability often gets confused with basic heart rate, which is measured in beats per minute. Heart rate variability differs by measuring the actual time difference between heartbeats.
So on an electrocardiogram we R-to-R (R-R) intervals and from breathing patterns there is variance between successive R-R intervals. And what heart rate variability is doing is capturing those changes between those heartbeats.
So it is a little bit more specific of a measurement but it is not dissimilar from basic heart rates, so people shouldn’t get too confused with it.
[Damien Blenkinsopp]: So could you give me a quick overview – what is heart rate variability, HRV, and how do you use it? What is it all about?
[Andrew Flatt]: So your resting heart rate is generally not consistent. We learn in a textbook that a heart beats approximately every 0.8 seconds for an average of 75 beats per minute. What that doesn’t factor in is the actual changes in heart rate, the subtle changes that, in response to respiration, where when you breathe in your heart rate actually speeds in a little bit and when you breathe out your heart rate will slow down. And that is normal.
That is called respiratory sinus arrhythmia. And essentially what heart rate variability is capturing is those subtle changes in heart rate in response to respiration. So heart rate in beats per minute is kind of giving you that average of how many beats there were, whereas the variability is telling you how much variation there was between the beats.
Now, there are various statistical procedures and so forth that we can assess variability. There is a standard deviation, there is the Rubian square, there are spectral analyses. So there are various parameters for heart rate variability but in a nutshell it is just measuring the variance and changes between the time interval between heartbeats.
[Damien Blenkinsopp]: Right, and you brought up a little bit of terminology there – it is R-R intervals, which is basically R means the top of the beat, the kind of spike of the beat that you kind of see on the electrocardiogram, so R-R just means the time in between beats, correct?
[Andrew Flatt]: Right, because they are such high peaks it is really easy to measure the interval between them so that is generally why the R-R intervals have been used.
[Damien Blenkinsopp]: Right, and just out of interest, why is it called an R? Why isn’t it called a beat?
[Andrew Flatt]: The peaks are just alphabetically named. There is the P, QRS complex, the T-wave, so – we just –
[Damien Blenkinsopp]: And the peak just happens to be the R, good. So I know that you have been using HRV in a bunch of areas to basically make better decisions, mostly about training. Could you talk about the different scenarios you have been looking at it with and where you find it most useful?
[Andrew Flatt]: Well, I think it just comes down to why I started measuring heart rate variability. I first learned about it just reading on some strength and condition forums, a website called [lead ips .com 00:03:22]. And there were some strength coaches talking about how they are using it with their athletes, so I kind of gained interest in it then.
But it wasn’t until I was preparing for a powerlifting competition and training was going really well. I was pushing it real hard and I was set to set some personal record at a lighter body weight when all of a sudden, I took a dive and I actually got a little bit of a cold. I took a few days off from it and I went back and hit the weights and things were just feeling real heavy.
And it was too close to competition for me to really fix things and I actually ended up pulling out of the meet and I was really disappointed. And I thought to myself there has got to be some kind of way that I can better manage my training and maybe kind of prevent this or see it coming a little bit better.
So that was kind of the motivation to actually purchase a heart rate variability device and start using it. So my original motivation was to guide my own training. I am involved in powerlifting so it was kind of a selfish motivation more so than working with athletes, but eventually that is kind of where it came to, where I would actually start using it with athletes.
I was training friends and colleagues and I would get them using it and look at their data. And that is kind of how things went from there.
[Damien Blenkinsopp]: So you obviously found it very useful, to have gone into an insight using this with other people now. So what kind of decisions do you make based on this? Is this is the only indicator you use? Is it the main indicator you use with your training program and deciding when to change up the variables?
[Andrew Flatt]: You know, when I first started using the device I was very skeptical at first. I didn’t know much about it other than what I read on the forms and what I actually did was for six months I used it and collected data, but I did not use it for any kind of decision making.
In fact, I really didn’t look at the trends or analyze anything until after about six months when I would kind of look at the trend and I would look at my training log and I would try to see what it was telling me in the first place. I think one of the biggest mistakes is people get a device and they think they know how to use it and then they want to start making decisions with it.
I think you almost want to do some kind of cross validation with it on yourself first and see what it is telling you in response to training or in response to different kind of life events – you get sick, you travel – what is it showing you? Is it meaningful? Can that drive better decision making?
And essentially, what I found was after six months of using it I would look back on it and after heavy training sessions I would see a decrease in my HRV score. Most noticeably I would see, after any kind of a new training stimulus, so being involved in powerlifting I wasn’t doing a whole lot of conditioning work but at the time I was doing my Masters, I was working with a whole bunch of other people.
In the weight room I was a grad assistant strength coach and they love to do conditioning on Wednesdays. So on Wednesday morning, we would go and run these stairs, and man, it was tough for me – being a power lifter and not running since I played football years before. And my HRV scores would just absolutely plummet after these sessions.
But after a few weeks I would notice smaller and smaller fluctuations in my scores and I was kind of reflecting the progressive adaptation for that training stimulus, and I thought that was kind of cool.
[Damien Blenkinsopp]: Right, so what kind of impacts do you see? So, once your score has plummeted, what does that mean the next day? Say you start the day and you track your HRV and your score has plummeted, what does that mean in terms of how you are going to be feeling? What does that mean in terms of how it is going to change the decisions you make that day?
[Andrew Flatt]: A low score can definitely be the result of a heavy training session. Unfortunately it is not that simple. One of the great things about HRV is also one of its downfalls, that it is a global marker of stressors, whether that is physical, mental, or chemical. So not always will you see a low score because of training, it can be brought on by other things. So you really need to be tracking other variables to really make a meaningful interpretation of what the data is telling you.
[Damien Blenkinsopp]: Right, so in the context of your training program, if nothing else changes it is kind of like that it then should be down to your training?
[Andrew Flatt]: Right, so I think one of the main things is are you an aerobic athlete? Are you an anaerobic athlete? Are you a team sport athlete? It depends on your training because what heart rate variability is, is it is a reflection of the cardiovascular autonomous nervous system. So for the most part, and especially within the research, it has predominantly been used with aerobic athletes and that is kind of who would most benefit from it.
I mean, resistance-training athletes, at this point it is all experimental to see what it is we are actually showing but it doesn’t necessarily reflect muscle soreness. It doesn’t necessarily reflect muscle damage or your neuromuscular abilities for that day, your CNS potential. It is a reflection of the cardiovascular autonomic nervous system, which is still a very important piece physiologically for being prepared for training.
So it is only one marker to consider the cardiovascular system is extremely important with the recovery process, with removing waste products, and so forth. So when the cardiovascular autonomic nervous system has kind of rebounded back to baseline levels or super-compensated to above, that would indicate that system is ready to go and it is more likely to be in a more adaptive state to any kind of physical stress.
[Damien Blenkinsopp]: Right, so you have mentioned that it is the autonomic nervous system and another thing that we often hear is that it is an indicator of vagal tone. What does that mean?
[Andrew Flatt]: So the autonomic nervous system, simply put, is divided into two branches – you have your sympathetic branch and your parasympathetic branch. The term ‘vagal’ is referring to the vagus nerve, which is essentially the parasympathetic branch of the autonomic nervous system.
You have parasympathetic innervation in the heart that essentially – in any kind of physiology class your professor will give you the car analogy, where if your foot is on the brake the car is not moving, and that is your rest and response. And the autonomic nervous system is taking care of all the things that we don’t consciously control – so our blood pressure, digestion, endocrine gland secretion, and so forth. And then when you take that foot off the brake you have that withdrawal of parasympathetic or vagal activity.
Then when you hit the accelerator all of a sudden you get that sympathetic output and that is going to actually increase heart rate and prepare you for any kind of stressful events, whether it is exercise or simple postural change from lying down to standing up. You have to pump blood to the brain so you don’t pass out and that is a sympathetic response.
[Damien Blenkinsopp]: Right, and another way I have heard it described it is that basically your parasympathetic is trying to balance your system so that the vagal tone is the ability for you to balance and respond to stressors around you. Is that another way you look at it, or is that not correct?
[Andrew Flatt]: Yeah, so essentially the sympathetic nervous system will be quite active during physical stress like exercise and then to recover from that is when your parasympathetic nervous system will help rebuild structures and repair the damage essentially that occurs during those stressful events.
So that is why measuring your parasympathetic activity on a day-to-day basis is a reasonably good indicator of your recovery status. If your body is still stressed from training and you have a higher sympathetic output or even just parasympathetic withdrawal, you know that your system may not be fully recovered.
Now, what I want to be clear is that it doesn’t mean that you can’t train if your HRV is a little bit low. And a lot of these apps, what I think people need to understand, is only measuring parasympathetic activity through a timed domain measured called RMSSD. So that does not give you any indication of sympathetic activity. It is purely vagally-mediated, so parasympathetic.
[Damien Blenkinsopp]: So just a couple of other terms that you hear quite a lot is LF, low frequency, and HF, high frequency. As I understand it they often say LF is the sympathetic stressor and HF is the parasympathetic relaxation. Is that true or is it more complex? Some of the apps track the LF and the HF as well, but some of them don’t.
[Andrew Flatt]: So the way you are talking about it, they are called spectral measures from frequency domain analysis. HF generally does indicated parasympathetic activity. LF actually would be indicative of both parasympathetic and sympathetic activity. So it is not as clear as we would like it to be, where HF is parasympathetic and LF is sympathetic and it gives you an indication of sympathovagal balance, they call it.
It isn’t that clear and one of the issues with the spectral measures that you are referring to is that in terms of their practicality and field settings, they require longer measurement durations for a valid assessment. These are less reliable markers on a day-to-day basis so it has kind of been recommended that RMSSD is the preferred parameter, especially for convenience and non-expert users in the field that just need a simple number that they can read and interpret real easily. The RMSSD value is preferred for that.
[Damien Blenkinsopp]: So is RMSSD the one that has the most research behind it?
[Andrew Flatt]: Well with RMSSD, the reason why it is preferred is that it is a more reliable marker. It is very easy to calculate. If you have R-R intervals you can actually calculate RMSSD in Excel – it’s a statistical measure, root mean square of successive R-R interval differences, that is what it stands for. It is consistent in paced or non-paced reading situations, where as HF and LF are going to be a lot more influenced by your breathing rate.
So, for in the field with athletes who may not be sticking to a certain respiratory rate or whatever, it is not going to affect your numbers as much. And lastly, I kind of got to it before, is it can be calculated in a relatively short time frame. In fact, you can get an RMSSD measure in ten seconds; however, that generally isn’t enough R-R intervals to capture a real window of that autonomic activity.
So actually part of our research was seeing what is the shortest timeframe we can measure HRV in with RMSSD and what we did was we found 60 seconds to be no different than a criterion measure, which has been established as five minutes. So we essentially randomly selected 60-second segments within a five-minute ECG and we found no differences. But when we looked at 30 seconds and 10 seconds there was less agreement with the five-minute measure. So our conclusions were that 60 seconds was probably enough time to get a valid HRV reading with RMSSD.
[Damien Blenkinsopp]: That’s great, that’s very short. A lot of the apps, you said, do a lot of the standard – I think it just comes from the research, which is five minutes for a recording. But a lot of the apps now are looking at like three minutes or something like that. What kind of variance do you see across the apps? Have you seen any apps that go as low as 60 seconds, making it a lot more convenient?
[Andrew Flatt]: Yeah, there are some apps – ithlete, for example, is an app that uses a 55-second test. There is another app call HRV4Training that uses – it actually allows you to select your test duration so there is a 60-second option. I believe there is a two-minute option, a three-minute option. And then I think there is a device called Tink that I believe is a 40 or 45-second test. I used that briefly. And the other apps tend to use a little bit longer.
Now, the longer measurement is certainly not a bad thing to get a bigger sample of R-R intervals for analysis. The issue comes down to is the athlete or the client – are you willing to do that every day? If it is two or three minutes, that can be a little bit long. Fifty-five seconds or one minute, that is generally not too bad. I find it more tolerable with the athletes I have used it with. Generally they can handle it, so it call comes down to preference, right?
[Damien Blenkinsopp]: Yeah, totally. So we talked a little bit about the apps. So I would like to dive into that because I know there are quite a few out there and there are a lot of them coming into the market now and HRV is just starting to become pretty popular. So basically you are going to have a device for tracking your heart rate and you are going to have an app to go with it. Which ones have you looked at and what are the tradeoffs and benefits of each? Have you got preferences and so on?
[Andrew Flatt]: So I first started out with the ithlete app. That was the one I read on the forums that people were talking about. In fact, I think it was the only one available at the time.
[Damien Blenkinsopp]: So when was this, by the way?
[Andrew Flatt]: This was 2011, early. I think around summer 2011 is when I actually bought it. So that specific device at the time required a heart rate strap and a little ECG transmitter/receiver device that you would actually plug into the headphone jack of your mobile phone. And again, it was a 55-second test and I have stuck with that device.
There are a few reasons why I have stuck with it, one being that it uses such short measurement duration. And especially now that I have looked at the data, I am quite confident that short of a duration is still going to give acceptable measures or more valid data. So I have stuck with that but I have used others. I have done some beta testing for some people and looked at some other apps. And at the end of the day you just want one that you are going to be able to use and that provides your data that is easy to interpret, nice visual trends, health, or whatever is more affordable for you.
There have been some advancements in technology that allow you to measure HRV without an ECG receiver. Now you can just use a Bluetooth heart rate strap with some of these devices. There was recently validated, a pulse wave finger sensor that ithlete is using that you can literally without any kind of heart rate strap you just plug your finger into this little finger sensor device that is plugged into the headphone jack and you can actually get your heart rate reading from the pulse at your fingertip.
[Damien Blenkinsopp]: How accurate do you think that is? Because I used one of those for something called Heart Math, which is using HRV but in a different area and that uses your ear. So it is collecting your pulse from your ear. But I find that every time I move in any little way that it is messing with the signal and it is not very clear. So do you find the finger sensor? Because it is using light, right? So it is pulsing light in to see what your heart rate is. Do you find that reliable?
[Andrew Flatt]: I think we have about 15 athletes where we looked at the pulse wave finger sensor and compared it to EKG. They were soccer players, male and female. We did supine and standing positions. And it was accurate. It was more accurate in the supine position but acceptable agreement also in the standing position. So we haven’t published that yet. We want to collect more data on it. But I am pretty confident in it based on the data that I have collected with it.
Now the pulse wave finger sensor device, that is not putting your finger over the camera lens – where the flash goes. That is not what we measure, just to be clear.
[Damien Blenkinsopp]: So if someone is getting one of these apps, what would be your suggestion? So all of them are using RMSSD, I’m assuming. I know the one I am using, Sweetwater HRV plus a Polar H7 strap, so the heart rate with the Bluetooth that you mentioned earlier for an iPhone 5. So that works fine for me and that was relatively cheap to get off and running with. So I know that Sweetwater, for example, they take RMSSD and they modify it a little bit. They put it on this 1-100 index. Do the other apps modify this? Are there compatibility problems later if you want to switch apps and you can’t compare your score?
[Andrew Flatt]: So Sweetwater, or the SweetBeat app, I have actually experimented with and that, from when I used it, was providing various HRV parameters. It was giving you the HF, the LF, RMSSD, SDNN – numerous parameters of HRV, which is great if you know what those mean and how to interpret them. But I generally tell people to look at the RMSSD.
I know when ithlete started using a modified RMSSD value what they essentially did was they logged transformed RMSSD and multiplied it by 20, and that gives you a figure on a 100-point scale. BioForce uses that value. I wasn’t aware that Sweetwater or that the SweetBeat device did or not. I thought it was a raw RMSSD value, but I could be wrong.
[Damien Blenkinsopp]: I actually spoke to them one time, so it is definitely a modified scale version of it.
[Andrew Flatt]: Okay, so then they probably use that value or something very similar. Now, not all apps use that value. For example, Omegawave has a smartphone app and they are using their own algorithm to come up with a daily readiness score, so they are factoring in HF, LF, the HF-LF ratio, RMSSD, so it is not one parameter that they use. So there is difference among the apps and what they interpret. So it is something you would probably want to look into.
[Damien Blenkinsopp]: Right, and you probably don’t want to switch around too much once you have settled on one.
[Andrew Flatt]: Right, you find an app that you like. What is most important for the end user is I think the visualization of the data and how they can view it so they can see what their kind is like, how it is responding to their training. One of the things I really appreciate about the ithlete app is that it allows you to input your training load score, so depending on what kind of training you are doing or how you choose to quantify your training load you have your RPE values and you can calculate tonnage for weightlifting or powerlifting.
You can do a trim value for endurance athletes or what have you. So you can input a training load value and then it also gives you the ability to track your cyclometrics, you perceived level of stress, sleep quality, muscle soreness, mood, your nutrition. There is a sliding scale for that you can kind of rate. So all of a sudden you have a device that isn’t just tracking your HRV but it is kind of monitoring several variables which really makes interpretation of your HRV trend more meaningful. I know BioForce has an online system where you can go on, input your data similar to the ithlete one.
I am not sure if you can do that from the app or not at this point but it is a very similar system. So that is another great product to look into. So when you are evaluating what app you want to use, you want to look at what additional features it has to offer because an HRV score by itself is less meaningful without all this other information. So the more information you have and that you can maybe attribute your changes and your trend to, the better off you are going to be.
[Damien Blenkinsopp]: Right, I know for me there have been a few times where there has been a huge crash and I have been wondering what happened. I didn’t have a big training session or anything yesterday, so it is definitely like this little investigation sometimes – why did my HRV crash? I know you have got some interesting stories about times that you have seen athletes or your own scores crash. What kind of things have you seen the influence where it crashes? Have there been any times where you really didn’t find any reason for it?
[Andrew Flatt]: I mean, if we are talking a substantial decrease in your score, usually it is pretty easy to attribute it to something. Sometimes it is these smaller deflections where you are like, you know, I am kind of surprised it is that low today. That may be harder to attribute to something specifically. But if you wake up with fever, you are going to have some real low scores and your heart rate is going to be high and you are going to have some low scores.
One of my coolest little anecdotes that I have with using an HRV app is when I got real sick a couple years ago over March break and HRV I was able to use to guide my training to where I could kind of start pushing it hard again and kind of get back to my normal routine.
For a week I had terrible symptoms. I had fever, I wasn’t able to train. My scores were really low. Once my symptoms kind of subsided and I wanted to get back into training, what I was seeing was from very moderate workouts, very low-intensity, something I would consider like a D-load type of workout, these were causing pretty substantial decreases in my HRV so I could see that my body was reacting to the training. But it was quite stressful, according to those scores.
So I would actually continue to train relatively light until my scores wouldn’t fluctuate so much and that is when I would actually start pushing harder again and I could see in my trend that it wasn’t as stressful. I wasn’t seeing as big of swings in my scores and I was kind of able to guide myself out of that situation where typically a meathead like me, I will just start pushing the weight as hard as I can as soon as I feel ready, which may not have necessarily been the best thing to do at that time.
[Damien Blenkinsopp]: Right, totally. I have been in similar situations myself. I know I had a score of 80 just recently and it crashed to about 50. I don’t know if that something you see often?
[Andrew Flatt]: Yeah, that’s a big drop. Were you able to attribute that to anything?
[Damien Blenkinsopp]: Yeah, I have been suffering from a chronic illness and it has something to do with that, so it is pretty serious. It is a pretty serious thing, it is not a typical thing. So in terms of someone a bit more normal, who is not dealing with medical issues or anything, what would a typical rash look like? Is it 20 points?
[Andrew Flatt]: Everyone is individual and unique. Every individual’s data needs to be taken in the context of what kind of training they are doing, how advanced they are, how trained they are. A more advanced endurance athlete, for example, will see smaller swings more than likely. They will recover faster.
You take an untrained individual and you put them through an intense workout, whether it is weights or conditioning, and they are going to see a big drop. That can last for 48 to maybe 72 hours. So every situation is unique and every individual really needs to take some time to collect some data and observe how their trend is evolving in response to their training because unfortunately you can’t just say that this means that for everyone, because that is just not the case.
And you really do have to maybe do some calculations with your data in Excel, looking at the weekly mean value. You look at the variance within that week and all that kind of analysis will give you a better indication of how you are responding to your training.
[Damien Blenkinsopp]: So of course, a lot of the other things that athletes look into when they are training are all sorts of lifestyle factors that could be affecting their recovery and how they are performing. I know that you have had many experiences with this and in one post you talked about travel and in another you talked about going home for was it Christmas or Thanksgiving? And seeing some stuff there.
What kind of situations have you seen – like another guy who went on Spring Break and he was partying a bit? What situations have you seen that could be said to be obvious, but what kind of things would you say to look at? Just typical things that you have seen affect it.
[Andrew Flatt]: Yeah, so your lifestyle absolutely will affect your HRV responses. For example, working with a soccer team, we put them through a hard week of training and we see pretty typical HRV responses and then half of them go out on Saturday night partying, maybe having a couple of drinks, I don’t know. And the other half maybe stays at home, gets to bed at a reasonable hour, and you can definitely kind of predict who was out that night based on that.
Now, you definitely would need to do a little bit more investigation. You can’t just look at a score and say, ‘This person did this.’ But it does give you some kind of indication that maybe you have to look into what is going on. Was it the night before a game? How are your athletes behaving?
Not necessarily a tool to spy on anyone or anything, but it kind of will lead to some questions. Why isn’t this person recovering? Why are their scores low? Are they getting sick? Are they staying up too late? Are they not getting enough sleep? Sleep is definitely one factor that will affect your score. Alcohol – if you are out drinking you are definitely going to see some lower scores the next day.
Like I said before, with illness your scores will definitely drop from that. In my experience any time I have gotten a cold or especially a fever, the score has dropped. Now you were referring to some of my older posts where I talk about I actually went home to visit some family that I get to see maybe once or twice a year. And I actually had really high scores the next day. Is that the reason why they were high? I don’t know, that is just speculation.
But anything that you perceive to be very restful, whether that is sauna, you get a book and read outside, get some sun – something that you perceive to be restful and relaxation is generally going to promote some of that parasympathetic activity and that restoration that we want to get. So I think it depends on the individual and their own personality for what they perceive to be regenerating and relaxing.
[Damien Blenkinsopp]: Well certainly sometimes I will take a specific day off and say okay, I am going to recover this day because I need to because my HRV is down. And it definitely pushes the score up, I have seen that many times. So like you say, the relaxation could be different for different people. But it definitely seems to impact the score if you take a day off and forget the work and all the other stressors. I don’t know if you have seen examples of work stress figure into this?
[Andrew Flatt]: I have seen some studies. I am not as interested in that so I don’t pay too much attention, but there is definitely a stressful lifestyle, whether that is from work, you can have money problems. These are all things that can affect your autonomic nervous system. So it can be apparent in your HRV score. One thing I found is just within the literature but also through trial and error, that some light aerobic work has a stimulatory effect on parasympathetic activity. So some active recovery can really help get people’s scores up.
In fact, just a few weeks ago I was going through kind of a work capacity phase where I was just trying to get in better shape, bring up my aerobic fitness a little bit, so after my resistance training sessions I was doing 10 to 15 minutes on the bike, on off days I was doing 20 minutes on the treadmill or 10 minutes on the treadmill and 10 minutes on the roller, just trying to increase my fitness a little bit. And I have actually never seen anything like it in my trend before.
I wasn’t seeing any really big swings from day to day, even after a heavy resistance training session with five sets of five with 80% plus. Normally that would result in a lower score the next day but it appeared that these smaller aerobic sessions really attenuated those swings day to day so I was seeing very little variance between my scores for that two-week period, but then as soon as I stopped keeping up with that it went back to my old-fashioned hard workout and you see a lower score and it takes a day or two to come back up.
So it is interesting how much of an effect just light aerobic exercise has on stimulating that parasympathetic activity. There is definitely a threshold where too much or too intense and it will have the opposite effect, but a reasonably late session for not too long generally has a stimulatory effect and you will see a bump in your HRV 24 hours later or so.
[Damien Blenkinsopp]: So are you saying that is something that is going to help people? Or is this just modulating the HRV but it is not going to impact your actual recovery? So it is just modifying the number but it is kind of hiding the fact that your HRV would have gone down?
[Andrew Flatt]: Well, I think again it comes back down to what your training goals are. Now after a heavy squat session and I do some cardio, some light aerobic work after, and I don’t see a drop in my HRV, that doesn’t mean I am going to be able to go squat heavy again necessarily. It is just saying that my cardiovascular autonomic nervous system has rebounded back to baseline level, so that system may be ready to go again. So again it comes down to context.
If you are more of an endurance athlete it would probably be more of a marker of when you are ready to train again, but with resistance training there is muscular damage. That isn’t necessarily reflected in your HRV. There is just not enough data yet to show that an HRV score is related to any kind of nervous system potential for strength scores or power or anything like that.
[Damien Blenkinsopp]: That is interesting because one of the things you mentioned was that when you are doing something new, some kind of new activity, some type of new training, that you see your score crash down in particular in those situations. Is that – do you think it is because of neuromuscular or metabolic adaptation that has to take place there? What do you think that is down to?
[Andrew Flatt]: Probably a combination of everything. You have introduced a novel stimulus that your body hasn’t necessarily adapted to yet or in a long time so it is just harder to recover from. I don’t have the answer for that. It hasn’t really been, at least I haven’t seen anything to explain why – that is just how it is. A novel stimulus, whether it is conditioning, resistance training – if you do a drastic change in your volume or intensity, from what I have seen it is going to cause a lower score than typical. But with persistence and that new training modality or those methods you will see that progressive adaptation and you will see smaller swings after the body kind of adapts. It gets more familiar with it. There is probably a better scientific explanation, I just don’t have it for you right now.
[Damien Blenkinsopp]: Great, so I want to talk about recording – how you record it, what kind of numbers you want to make sure you get, frequency, and so on. But just before that, how about baseline? Can you increase your baseline over time? Or are we just looking kind of like at the dips and the highs and trying to keep it in the highs more and slacking off when we have more of the dips? Or are we able to actually influence this and in a way build more resilience over time?
[Andrew Flatt]: Your lifestyle is going to change, your training is going to change, your training frequency. If you are a competitive athlete that you have different seasons, different times, that is all going to affect your HRV because your training is going to change. You are not going to always be doing the same type of training. You might be doing less aerobic work in a different phase and that aerobic work is really what stimulates those higher HRV scores.
So if you are doing less aerobic work you are going to see lower scores. So you do have to take whatever your baseline is – you have to take it into context for that training phase and your new training goal, so you absolutely have to have an evolving baseline. A lot of the apps will use a rolling 7-day average but generally at the start of a phase you look at your first week, you look at the average, you look at the variance within that week.
A simple value to use is called the coefficient of variation. It is just the standard deviation divided by the mean times 100, and that gives you a percent value of the variance, and see how it evolves from there.
[Damien Blenkinsopp]: So what do you use the COV for?
[Andrew Flatt]: So the Coefficient of Variation is where you have a weekly mean value, which is just the average of a 7-day period. That average doesn’t necessarily indicate or reflect how much fluctuation existed between those scores on a day-to-day basis, right?
So we want some kind of value or figure similar to a standard deviation of how much variance there was because let’s just say your average between two weeks is no different, but you have much more fluctuation in one week than the other – well, that could be indicative of some positive adaptation or I have a case study that we did with a cross country endurance athlete that should be published in one of the next editions of Australian Strength and Conditioning.
We actually found that his CV value, the coefficient of variation, was much more related to his endurance performance than his weekly mean value. And we get into possible explanations of why in the paper but the variance is important.
[Damien Blenkinsopp]: So you want less variance, which means that your system is dealing with the different stressors and it changes more easily?
[Andrew Flatt]: I don’t think – I think it is a matter of maybe when you want that. If you are seeing big fluctuations in your scores that is not a bad thing. That is your body adapting and adjusting to the training. But that probably means that you are not in the best state to compete at your best or to perform at your best because your body is adapting and it is going through the stress and recovery phases.
But all of a sudden you have been doing that training for a while and you see less fluctuation in your scores and there is maybe less – it is not the same amount of stress as your body initially perceived it as and had you recover from. You may be in a situation where your performance – you may be at a higher level of performance.
[Damien Blenkinsopp]: Yeah, it sounds like COV low variance could mean that you have adapted to whatever stimulus you are giving yourself, and that could be lifestyle or it could be training. And in another situation if it is pretty high it could mean that something different is going on and your body is adapting to it.
If it has got high variance it could be a good thing if you are going through these training sessions. It is showing that your body is going through that adaptation, does that makes sense?
[Andrew Flatt]: Absolutely. And one thing I need to point out is I started using the COV value after reading a case study by Daniel Plews and Martin Buchheit and all those guys that are the experts in this area. And what they found with the CV was in an overtrained, high-level endurance athlete I believe the CV was related with the progression of overtraining.
So when you are looking at any kind of value, whether it is the mean or the CV, you really need to look at the training load. You need to look at their perceived levels of fatigue and stress to really give more meaning to that value. So again, a high HRV score or an increasing trend can also be indicative of overtraining and mostly in endurance athletes. So you kind of have to look at these other factors.
The HRV scores alone aren’t going to tell you much without all this other information. So the CV, whether it is good or bad or whether we want it or not depends entirely on the context of that training and what is going on with the athlete and how far we are from competition, so there is no such thing as we want this, maybe in certain phases we want this, but it is all relative to the individual and to the training, so everything needs to be factored in.
[Damien Blenkinsopp]: If you take two athletes or perhaps an athlete and a non-athlete and you compare their HRVs, their 7-day average right and getting their baseline, are they going to be different? Is the athlete’s going to be higher? Is that something like going back to your baseline, is that something you want to be higher or you should be trying to get higher over time. Is it possible?
[Andrew Flatt]: I mean, the average person, just for the cardio-protective benefits of having a higher parasympathetic activity at rest definitely generally higher HRV is a good thing. If you take a team of athletes and you have them monitor their HRV, you are going to get different scores and a group of female soccer players that I work with over this past season, their average scores range from the low-70s up to a couple of girls that were pushing 100.
There is a genetic factor here. There is lifestyle, there is fitness. All these things come into play and you can maybe generalize that an endurance athlete who has a very low resting heart rate is going to have higher HRV, which can be in the 90s plus anaerobic athletes can be between the 70s and high 80s, depending on their fitness level.
So you could maybe say that this would be where the average would be for this type of athlete, but in my experience everyone has kind of have their own trend and their own response to training – similar responses in terms of the fluctuations in following a heavy training day and whatnot. But you are not going to get a team of soccer players with everyone’s score at 90 with similar changes, everyone is different. And you should plan accordingly for that.
[Damien Blenkinsopp]: Right, so for someone in the 60s, is that okay? Or someone in their 50s?
[Andrew Flatt]: Well, I mean I would ask if that is being measured in a supine, lying down position or if that is a standing value, because that obviously will make a difference.
[Damien Blenkinsopp]: Let’s get into that then, because I know you take both readings, correct?
[Andrew Flatt]: Well, I have experimented with both. I have been sticking with standing – I had been doing it standing since day one but I did an experiment for a little bit and actually at different time points I experimented with supine readings as well. So you want to get into –
[Damien Blenkinsopp]: So I mean, supine just for the guys listening – that just means you are lying down? So you are taking readings when you are still in both situations, right?
[Andrew Flatt]: Correct.
[Damien Blenkinsopp]: So we are getting into sort of recording methodology here. How do we go about actually taking these readings and when would you do it to get reasonable results? I take it, for instance, every morning when I wake up and I will take the lying down one and then I will stand up and take that. I have to let it rest for a little while, so I will stand up for about a minute and then I will take the reading.
So you can tell me if that is like correct or not. I seem to get relatively stable readings. How would you go about it now? What kind of things have you discovered that are good and bad and help to get and what kind of things do you need to avoid?
[Andrew Flatt]: Well, it’s interesting. The general guidelines are a supine measurement where you record the last five minutes of a ten-minute segment, so you essentially have what I often call a stabilization period where you let your heart rate adjust to that position.
So that is generally a five-minute period followed by a five-minute recording. You know, with the research that I have been doing at Auburn University with Dr. Michael Esko is trying to investigate shorter, more convenient HRV recording procedures because one, we want to do research with these smartphone apps but we weren’t entirely sure if we were going to be able to publish anything without any kind of validated shorter measurement procedures that we could say, ‘You know what? We did a shorter measurement recording. We had a shorter stabilization period.
But that is not necessarily a problem because it is not really showing any differences to these accepted standard measurement procedures. So as I kind of mentioned before we found that 60 seconds was a suitable duration for an RMSSD measurement. We have a new paper that is currently in review where we looked at how long does this stabilization period need to be, at least in a supine position?
So we looked at a standard measurement – five minutes following a five-minute stabilization period. And we just looked at if each individual minute – you know, minute one, minute two, three, four, and five – were those values any different to the five to ten-minute segment? I am not able to reveal the results but I am pretty confident that we can get away with a shorter stabilization period, much shorter than what is traditionally recommended. And we are just looking at capturing a resting measure and we are not using this for clinical diagnosis or anything like that, right?
So in healthy populations in athletes where we just kind of want to get a general indication of their heart rate variability that day and we don’t need a whole ten-minute procedure.
[Damien Blenkinsopp]: So what is the statistical variance we are talking about between yours and the five-minute one? Is that 5% difference?
[Andrew Flatt]: Are we talking about the stabilization or the 60 seconds?
[Damien Blenkinsopp]: Yeah, if you do your shorter version. Which is one minute and one minute?
[Andrew Flatt]: Let’s just say that you use a one-minute stabilization period and then a one-minute test. I mean, you are trying to get me to get into the results, which I shouldn’t do until it gets published.
[Damien Blenkinsopp]: Just a rough idea. You said it is okay, right? Don’t give me a statistic yet.
[Andrew Flatt]: Let me putting it this way, it would be trivial. That’s the term we use with that statistic called the effect size, which is telling us how practically meaningful the difference is. The shorter stabilization period as opposed to the traditional one, you would probably see trivial differences.
I could tell you within the literature a five-minute HRV recording has been used following only a one-minute stabilization period and that has been used in elite endurance athletes and the data was still providing very meaningful information pertaining to training status so again, a shorter stabilization period of one minute has been used so I would say to go ahead and use the one-minute stabilization period.
[Damien Blenkinsopp]: So it sounds like it is reasonable to do a one-minute stabilization and a one-minute – depending on the app they do different times or automatically of course, but you think that would be okay for some guys at home who want to use this for training and so on?
[Andrew Flatt]: I mean absolutely. With the athletes I work with and with myself and then with the data that we collected and looked at, the one minute is not very different from the five-minute value. So yeah, I am quite confident in that shorter measurement with RMSSD, specifically.
[Damien Blenkinsopp]: Great, so what other things – are you still taking the lying down, the supine, and the standing – and the one we have just spoken about, the one minute, one minute, is that just fine for both of them?
[Andrew Flatt]: Yeah, after a postural change what happens is in the supine position your heart doesn’t need to work as hard to pump blood to the brain. Then you stand up all of a sudden you have receptors that are going to detect changes in blood pressure and this happens real quickly, but essentially your heart rate is going to shoot up real high immediately following a postural change.
And then it actually takes longer than a minute to actually stabilize, but in the research one minute following that postural change is when they will start recording HRV in the standing position. Going back to why I like the standing measurement, it is simply because what’s happening is you are introducing a small stressor to the body that it needs adapt to. It is called orthostatic stress, when you stand and put that little challenge on the heart where it has to react to the postural change and then you essentially are evaluating how your heart is responding to that.
If your heart rate variability is very low after you have given your heart rate time to stabilize, that may be a better indication of how your body is going to respond to physical stress that day. That is kind of a working theory. And that is nothing new. I am not sure if you are familiar with what is called the Rusko test, where you start by measuring the heart rate lying down and then you measure it following a postural change at different times, and you are trying to see what the changes are between those. So it is not a new concept and certainly nothing that I can take any kind of credit for.
But I did experiment with taking supine and standing measures and seeing how it related to my previous day training. This kind of unequalled one experiment – I have always found that the standing position provided a better reflection of my perceived level of recovery with yesterday’s training. That is not a very scientific method and I didn’t take any blood markers or anything like that but just from visualizing the trend I see that the standing position looks how it should, based on how it is feeling and what training was like the previous day. So I have pretty much stuck with that.
[Damien Blenkinsopp]: Okay, so now do you use just the standing or do you use both?
[Andrew Flatt]: Yeah, my preferred position is seated or standing. I do standing just because it is practical. You wake up, you go pee, you are already standing. I use the finger sensor now, so I plug in the finger sensor and I do my measurement right there in the bathroom. It is just easy.
The seated position would also be similar to provided that. You are obviously going to have to sit up and there is going to be that little orthostatic, that seated up, more vertical position challenge. So the seated position is probably – I wouldn’t think it would provide significantly different in terms of at least the trend. The number value might be different but the trend would probably be the same.
[Damien Blenkinsopp]: Do you see more variance and slightly lower numbers for standing versus supine, or lying down?
[Andrew Flatt]: Absolutely. The supine values are going to be much higher. I have data on the soccer team I have been working with. I had them do supine and standing measures because that is a question I have always been very interested in – what is the better position?
Some preliminary analysis on the data – I think what we’re seeing is that without getting too much into the results I think supine and standing may be potentially indicating some different information where supine may be related a little bit more to fitness and standing may be more related to the acute changes in response to previous day’s training.
Again, that is very preliminary and we have still got a lot of analysis to do but from that data that is kind of what I am seeing. From my personal experience –
[Damien Blenkinsopp]: So what you are saying is that lying down is kind of like your baseline and standing is what has been going on the last week in terms of what you have been up to and exposed to in terms of stressors?
[Andrew Flatt]: Possibly. It is hard to draw any kind of conclusion. But in the supine position in very fit athletes there have been issues of parasympathetic saturation, but all of a sudden you sit up or you stand up and you kind of eliminate that issue. So I know in a recent paper by Stanley Peak and Martin Buchheit where it was in sports medicine and they reviewed the literature on parasympathetic reactivation after exercise. And one of their recommendations was to measure in a seated position.
I would definitely recommend anyone, especially exceptionally fit athletes – any endurance athletes or some really fit athletes like soccer players, rugby, or what have you – with really low resting heart rates. I would definitely do either a seated or a standing position. For less fit individuals with higher resting heart rates, the supine position may be fine. That is a gut instinct and I don’t necessarily have the kind of data to support that. So take that how you want to.
[Damien Blenkinsopp]: Okay, a few of the other things – just to make sure there are no other confounding variables coming in here – do you have to make sure this is at the same time of day, or is that irrelevant?
[Andrew Flatt]: Actually yes, I meant to get into some of this stuff. You definitely want to be consistent with your measurement procedures. One of the best recommendations is you have to remain as motionless as possible. It is funny, you collect ECG data on a bunch of athletes and you are reviewing it and you see some funny things and you are like, ‘Man, what were they doing in there?’ And one athlete had a bit of a cold at the time and we could see her sneezes in R-R interval trend.
On the tachygram we could see when she sneezed. We could see when athletes moved positions or adjusted their position. This all is going to affect your heart rate. I looked at an ECG trend when the investigator walks into the ECG room, or the lab, and just that startles the subject or it might not startle them but it does provoke a heart rate response and all that can affect your heart rate variability information.
So you want to be as undisturbed as possible. You want to limit any kind of noises. You want to limit anything that can be distracting. You obviously don’t want to necessarily check your emails or messages first thing before you do it because that creates an anxiety based on work-related issues or anything really.
So you definitely just want to wake up, do your business in the bathroom, empty your bladder, and do your measurement, whether you do it seated or standing or if you choose to go lay down again. Or if you choose to just do your measurement right in bed after you wake up, you know. Consistency is the most important, definitely limiting the noises, like I was saying.
Time of day is a research question that we have and that is something we want to answer. There is definitely going to be circadian rhythm effect so if you do a measurement at 7 a.m. it is definitely going to be different by noon. But is there a difference between a 7 a.m., a 9 a.m., or if you are within a reasonable time?
We have been asked by some professional NFL teams if they can bring their athletes into the workout facility, have them lie down on a training table, and do their HRV then, as long as they control for all the other variables. My assumption is that it is not going to be the same information you are getting from a waking measure, but how different is it and can we still get some meaningful data from that? I don’t know – that is something we definitely want to look into.
[Damien Blenkinsopp]: So the whole thing about doing this first thing in the morning is it manages to eliminate a lot of potential confounding variables like what is going on in your environment, what you have been doing in the morning, anxiety, and all these other things.
[Andrew Flatt]: Yeah, and apart from sleep it is going to be your most rested state, right? So that is the ideal time to do it.
[Damien Blenkinsopp]: So some of these apps also correct for things like arrhythmias, errors, artifacts, ectopic beats, and a bunch of things which are kind of noise. Would some of them, like I know the Polar kind of automatically does that. I am guessing that some of the others do. Does this eliminate these kind of things we are talking about to any extent or not?
[Andrew Flatt]: Yeah, because we did a cross-validation with the ithlete device and we looked into how it goes about interpreting the data. And actually that device particularly has thresholds for R-R intervals where basically the average highest range for an R-R interval versus the lowest range, if you get a series of R-R intervals that kind of exceed that threshold, either above or below it, it is going to correct for it with the adjacent normal cycle.
So a lot of these apps will have built-in irregular beat detection systems. Again, whether it is the R-R interval that is way longer than average or way shorter than average, it will essentially pretty much red flag that as an irregular beat or an artifact or what have you, and correct for it. And that is a limitation of a shorter measurement.
If you are doing a 55-second test and if you experience a couple of ectopic beats, generally within a one-minute period you should be experiencing more than one. But the shorter measurement duration, that is a shorter series of R-R intervals, and there is more room for error in that situation. But like I said there is that irregular beat detection function. When we have compared and I think we had 25 athletes where we compared it to ECG and it was accurate, and that small sample of people didn’t have as many issues.
[Damien Blenkinsopp]: Right, great. So is there anything else in terms of recording that you have to be careful of to make sure the data is useful and current and so on?
[Andrew Flatt]: I think the key is that you want to be able to do this every day and you want to do it consistently for meaningful data analysis and the key is to just make sure you do it and you are consistent in your environment and where you are consistent in your position.
You don’t want to stand one day and do it seated the next day and then supine. If you want to experiment, when you do a measurement save it in your preferred position and just log your other position measurement. You don’t want to save it so that it affects your trend line by any means.
So the key is being consistent in your position, being persistent if you choose to do the paced breathing. Some of these apps provide paced breathing. A lot of them will give you 7.5 breaths per minute, which was kind of the mean breathing frequency of a group of endurance athletes.
That is kind of where that value came from. Just be consistent and don’t do paced breathing one day and then not the other. It shouldn’t have too much of an effect with RMSSD but you do want to be as reliable as possible with your procedures. So either do spontaneous or paced breathing, pick one or the other and stick to it. Stick to the same position.
I am not going to like, I don’t necessarily measure at the same time every day. I mean, my lifestyle changes and I will be able to sleep in on certain days. I might have to be up super early one day and I do it when I wake up. That’s just the way life is, right?
Some people take it pretty seriously and they wake up at the same time every day and that is great. That would probably be more reliable but you have got to be reasonable.
[Damien Blenkinsopp]: Great, so what I do, for example, is I track it every single morning and I am looking for either acute drops, like big changes to take notice of. Otherwise, I am kind of looking mostly at the seven-day average. How do you approach this. Ideally I want my seven-day average to go up over time so that I feel like I am getting somewhere with things. How do you look at it? What is most important? Are you looking mostly at the seven-day average? Are you looking at the day-by-day? What are you using most in your actual decisions?
[Andrew Flatt]: Well, I like to look at everything. I like to see the acute change of what happened between today and yesterday. I do not generally at this point in time use a daily change to be a huge determining factor in my training, specifically because I am more of a resistance-training athlete.
I am involved in powerlifting, so an HRV score isn’t necessarily indicating if I am going to be stronger or anything like that. But I do take a look at it and I see and I always like to compare it to what happened the previous day. What I like to do is look at the weekly average and the variation of the previous seek, just to see how that corresponds to my training plan. If I had a higher-volume week where I was trying to create some fatigue, I would expect to see a lower average and maybe some more variation and go from there.
[Damien Blenkinsopp]: But if you didn’t you might say, ‘Okay, well I have been undertraining and I want to push a little bit harder this week.’ Is that the case?
[Andrew Flatt]: Yeah, I mean you can use that to guide how you may structure your next training cycle. Again, it really does depend on what kind of athlete you are. But for resistance-training purposes, I just do a lot of personal experiments.
I went through a phase where I was using the acute changes to guide my daily training, so rather than taking a – I would work three weeks harder and deload every fourth week. I stopped doing that for a bit where I would just reduce training loads on a day with a low HRV score, should that happen on a training day.
Training like that was fine and I made reasonable progress. I didn’t find that not deloading was an issue. Every fourth week by just taking off a day here and there or reducing loads. That was fine.
The issue is if you really want to make any kind of marked improvements you are going to have to do some overload training. And if you are doing overload training you are going to accumulate some stress. And you are probably going to see a decreasing trend in your HRV and that is generally not a huge issue. You just want to be mindful that you are starting to accumulate some fatigue and how long you want to persist with that. You want to pay attention to soft tissue issues. Are you getting a lot of inflammation? I would get some tendonitis in my elbows and so forth. So you use it as a guide but you take it with other parameters as well, like I was saying before.
Again, an endurance athlete would be a little bit different. I would actually probably use HRV – the acute changes. I would probably use that a little bit more to influence my daily training just because it has been shown that HRV-guided training with endurance athletes, based on your parasympathetic activity, you may be in a more favorable position for training for endurance exercise. So again it all comes down to what kind of athlete you are, what kind of adaptations you are trying to create.
[Damien Blenkinsopp]: Yeah, great. So looking at potential alternative metrics, another thing that people use a lot is resting heart rate. Is that something you would use as well or do you find HRV better? Is it ever worth taking both and looking at them in conjunction or do you think – what have done? Or do you have any experience with that, at resting heart rate?
[Andrew Flatt]: Well I think that resting heart rate is a little bit more crude of a measure. That is – now, although it is a little bit more prudent it can still be very effective. In fact, if you look at your RMSSD trend against your heart rate trend it will generally be a nice inverse relationship between them where they will kind of mirror each other. I personally don’t monitor both. I mean, if you don’t have an HRV device I would definitely do heart rate. I mean, that is something you could do by just measuring your pulse every morning. In my experience I just use the HRV value. What I want to do with the data we collected in the soccer team is see if the heart rate variability provided more meaningful information than basic resting heart rate alone. Do we even need heart rate variability? Even though it can be more specific of a measure, is it necessary? I don’t think that people need to dismiss heart rate and think that it’s not useful because it absolutely is. There has been good data on it and again, your heart rate variability trend with RMSSD isn’t going to be too dissimilar from your resting heart rate trend, it is just kind of inversely mirrored, you know?
[Damien Blenkinsopp]: Actually a couple of things, confounders I forgot to look at but I think are important. Our age and our gender, do they influence?
[Andrew Flatt]: Absolutely. What you will find as individuals approach middle age or they start to get a little bit older there is going to be a natural decrease in parasympathetic activity; however, that can be changed with training. So if you are doing regular aerobic work you can mitigate those decreases and have reasonably high HRV on a regular basis; however, I would assume that would change if you should stop keeping up with that kind of training, but absolutely. Generally what you will see is older individuals will have lower resting heart rate variability. Females tend to have – if you have two sedentary individuals the female will generally tend to have higher – that is not always the case.
In our data we looked at 20 endurance athletes – 10 males, 10 females. Their resting heart rate variability was not statistically significantly different so we measured them and compared them as a group rather than by gender. So if you are endurance trained you are going to have higher heart rate variability generally, whether you are male or female. But when you remove the training factor females will generally have a higher resting heart rate variability versus males – but again, that is not always the case, just generally.
[Damien Blenkinsopp]: I would like to talk a little bit about where this is all potentially going. In the future are we going to be able to do different things with HRV? Because I do know that it is getting more popular and there are more apps and devices coming out. What do you see happening with HRV over the next five years? Do you see it getting more sophisticated? Are a lot more people using it in different areas? What do you see?
[Andrew Flatt]: Well definitely in the clinical setting with regards to cardiac rehab guiding training of individuals who have had cardiac events and so forth, I am not as interested in the clinical side but that is kind of where a lot of this came from and started. So there is going to be a lot more usage of HRV in those situations, especially when we have validated mobile technology where you can acquire a resting score in a reasonably short period of time. I see it growing there.
One way that I see it being included in athlete is with reduced requirement, a lower frequency of measuring. So for example there is a recent paper that showed that less frequent measures of only 3 times per week was suitably reflective of the weekly mean value. So it didn’t necessarily need the seven-day value. You can get away with three when you are looking at the average.
One thing we are looking at with our data in the soccer team is how few days can we measure HRV where the mean value and the coefficient of variation are no different. So if we get more data on that and we start to realize that we don’t need to measure HRV every day if you are looking at the means and the CV. It becomes more practical and they are affordable. It was previously cost-prohibitive to measure HRV. You needed either an ECG or an expensive device. You needed an experienced and qualified technician to operate the device or the machine and then interpret it. Now within two minutes or less you can get an HRV score. An athlete can take it home and figure it out. It is real easy to do interpretation. Again, with the visualization and these other factors it is becoming a lot easier to use. So it is becoming more feasible for people and it is more affordable. So I can see it being definitely more widespread in sports, especially for any endurance athletes or soccer teams that currently aren’t using it. There are definitely plenty. But I think the more evidence that comes the more likely they will be to use it. Even the fact that we can now acquire HRV with a finger sensor makes it a lot more practical for an athlete to wake up and do the measurement.
If you think about it, a one-minute test is not that hard. But you would be surprised how many athletes can’t seem to do it every day. So reducing the measurement requirements to fewer days per week and making it easier to acquire the data, that is just going to increase the usage of it, I believe. It will at least increase the research where we will have more data to see if it is even worthwhile using in a soccer team or in a football team, and whatnot.
There are other areas where HRV is being used in the biofeedback where you are adjusting your heart rate, trying to increase your HRV prior to – there have been studies looking at baseball batting, golfing to see if it affects how accurate they are with their putts and so forth. That is not an area I am involved in by any means but that is where it is used.
[Damien Blenkinsopp]: Right, and I would say that some people have been connecting that to the flow stake, which they say is the high-performance stake. So the idea was that a higher HRV would mean that you are accessing your flow and you are more in a flow state than having a lower HRV. So I think that is some of the thing around that. I don’t know if you have seen that?
[Andrew Flatt]: Yeah, I have looked at some papers. My interest has always been in a resting measure and how it relates to performance and fatigue and so forth. But that research is progressing so who knows where that is going to evolve. But again, it is just a matter of having more published data to show that this is how it can be used. We are pretty clear that it is pretty effective but how practical can it be in the applied setting with a team of athletes and so forth is the next question.
[Damien Blenkinsopp]: So where is a lot of the research on this and which journals do you find it in? Are they in some specific journals or is it sort of scattered around? Have you seen it increasing over time?
[Andrew Flatt]: There has definitely been an increase in the amount of research on heart rate variability for athlete monitoring purposes and so forth. Just to name a few journals you are looking at International Journal of Sports Physiology and Performance.
There have been some in the European Journal of Applied Physiology. Every month there are one or two of these papers in a lot of these sports and science journals every month that pertain to heart rate variability. Journal of Sports Sciences, European Journal of Sports Science, Journal of Strength and Conditioning Research, so yeah – I kind of go through these every month and see what has been recently published. You can get on Twitter and follow a lot of these researchers and interact with them and sometimes they will give a heads up on what is coming and you can discuss it with them. Attending conferences, you can kind of see what research is upcoming, what is being done.
In fact, that is how I got into all of this. I attended the National Strength and Conditioning Association – their national conference in 2012. And that is where I met my colleague, who I have been working with for the last year or two, Dr. Michael Esko. He was presenting a poster on HRV and he was the only on there doing any HRV research. He was living in Alabama, I was living in Toronto. We hooked up and the next thing I knew I was moving to Alabama and we started doing research together.
[Damien Blenkinsopp]: Great, so who else might this be – you may have already answered this. I know you mentioned a few names, but who besides yourself would you recommend to follow to learn more about HRV and these biometrics?
[Andrew Flatt]: Well definitely Martin Buchheit. You can find him on Twitter. Daniel Plews, who worked with Dr. Martin Buchheit. Jamie Stanley, another guy who has been producing some great HRV research. Fabio Nakamora, Joel Jamieson, who kind of runs the BioForce system and the 8 weeks out website.
The ithlete has a blog where they discuss HRV research and maybe they have an endurance athlete that posts a training log. I try and post some data and some new research here and there. So on any of those social media sources like Facebook or Twitter you could generally find some of these individuals.
[Damien Blenkinsopp]: Great, there are a lot of good references there. So of course there is your blog, which is HRVtraining.com.
[Andrew Flatt]: Yeah, I try and update it every once in a while. Things get busy so I am not as religious with it as I used to be. But the whole purpose of that was to just share data and there wasn’t much talked about it and I wanted there to be.
So that is kind of where it has started and now it has evolved to I will discuss some of our new research projects and post some new research. But it kind of was started with just posting data and then trying to analyze it and leaving it open for discussion.
So if you are interested in looking at some previous trends of my HRV or HRVs of athletes, where we discuss and analyze the data or try to come up with a meaningful explanation or some research review and you can check out the sites. I should warn you that a lot of the older posts, I kind of reread some of them recently, and they make me cringe.
[Damien Blenkinsopp]: Isn’t that always the way?
[Andrew Flatt]: Take it with a grain of salt when you read the older posts. I have learned a lot since I started and I have learned a tremendous amount. So just be aware that some of the other posts may not be a current reflection of my thought process these days.
[Damien Blenkinsopp]: Of course. Coming back to more of a general view in terms of you personally, what would be your top recommendation to someone trying to make better decisions about their body’s health or performance with data?
[Andrew Flatt]: You need to select what monitoring variables you are going to monitor and you need to be consistent with them. And you need to do a lot of trial and error. You need to almost separate yourself from the data, collect the data, analyze it later with your training lots, and see what it is telling you. If a training variable isn’t meaningful, if it is not – if you can’t figure out why you are measuring it or what it is telling you, then you probably don’t need to do it.
You want something – so, for example, with me and the resistance training I am continually experimenting with HRV. There is just not a lot of data in resistance training and how you may be able to use HRV as a tool to guide your training. So I am consistently just experimenting with it.
But it is pretty clear in the research that perceived levels of training load, RPE values, perceived levels of stress, fatigue, muscle soreness – those things are worth tracking because they do correlate with other markers of fatigue and stress. They are just noninvasive. They are easy to monitor and you go with it.
I can’t tell you not to monitor certain things because it is fun. It is fun to collect data, it is fun to experiment. But generally if you are just in it to try and improve performance, you want to pick the variables that are the most meaningful to you, that are the most supported, and you need to be consistent with it.
[Damien Blenkinsopp]: What other data metrics, biometrics, do you track for your body on a routine basis besides HRV?
[Andrew Flatt]: Well I do, again, the perceived levels of fatigue, muscle soreness, and all that through the app. I will do training load and every now and then I will calculate my tonnage, where I will multiply the weight I have used by the amount of sets and reps and so forth and see how that relates to my session rating of perceived exertion.
If RPE better relates to HRV or if the tonnage value does – I don’t do that all the time. It is time-consuming to do those calculations. But regularly I do my RPE for my workout. I will do my perceived levels of fatigue and muscle soreness and so forth. And generally there is a comment section so I will usually make a note or two of something that happened the previous day.
If I was out and had a few drinks with some friends I will make a note that I had a few drinks. If I am traveling, when my training structure changes, things like that – I will make note of it. And I do keep a training log where I write down all my workouts and so forth. So there are plenty others that you can do.
[Damien Blenkinsopp]: So it sounds like you have a little diary related to stressors and health in general.
[Andrew Flatt]: Yeah, and again that is all stored right on the smartphone app that I use. The training log in my gym bag is just a little notebook where I log my workouts. I was going through a phase where I was going through a reaction time test and a tap test, again, with two different smartphone applications. Honestly, I was doing it at a time where I was less familiar with certain statistical analyses and I probably really didn’t know how to analyze the data very well, but it is definitely something I have been interested in.
There is some data to support that psychomotor speed assessed through a reaction time test can be related to fatigue and overtraining. So there is a smartphone app. I believe it is free. And essentially the screen will prompt you to react to a light changing on the app. So as soon as the light turns green, you tap it, and then there is an unknown time interval where it will then prompt you to tap it again over a series of five taps. And then it will give you kind of the mean value of your reaction time.
And I think the data is pretty cool, that I have read, and that supports it. I haven’t really seen any kind of longitudinal data where it has been done every day with athletes, so that is actually something I would actually like to include in a future study along with HRV and some other measures, this reaction time.
[Damien Blenkinsopp]: Yeah, great. There are a few of those apps and I know that some of them are free because I downloaded and played around with them myself. But like you I haven’t really gotten into it. I played around with it once or twice. So thanks for all this stuff, Andrew. This is very detailed and we have really done the topic of HRV justice, really tackling it from every area. So thank you very much for your detailed explanations on everything.
[Andrew Flatt]: Oh, it is my pleasure.