Andrew Flatt: Elite vs. Recreational Athletes & HRV Coefficient of Variation
Listen to the full episode here:
Andrew Flatt, MS, CSCS
PhD Student in Exercise Physiology at the University of Alabama, Researcher, Professor
Episode Resources and Links
In This Episode
- Coefficient of Variation or HRV CV
- Predicting fitness improvements weeks in advance
- Predicting competition performance
- HRV value differences in Elite vs Non-Elite athletes
- How coaches and teams should implement Heart Rate Variability monitoring
- Training adaptation specificity
- Difference in HRV changes from aerobic vs anaerobic
- Enhancing recovery with aerobic training
- Minimum effective dose of training
- Maximum effective dose of training
- How to avoid parasympathetic saturation
- Which position (seated or supine) to use when measuring HRV
- Determining when a stimulus is no longer sufficient for adaptation
- The impact of non-training related stressors
Jason Moore: In this episode, we’ve got Andrew Flatt, who is increasingly becoming a go-to name in the sports science industry due to his research on heart rate variability. Andrew is an exercise physiology professor at the University of Alabama where he is fortunate to have access to a wide variety of world-class athletes and is collecting and analyzing some really fascinating data. One of the big topics we discuss in a minute here is the different between elite athletes and recreational athletes and not only normal differences that you might think of but HRV value differences as well. More specifically, we’ll cover how to use various HRV values in relation to optimizing sports and athletic training. And again, this is straight from the mouth of one of the go-to experts on this subject, so I’m really pumped to share this.
A few of the topics we had include weekly mean HRV, what it is, how to use it, and how to use the coefficient of variation or HRV CV which you may have heard of before and how the CV number can actually possibly help predict competition performance. So it’s really interesting. There’s also a big difference in the coefficient of variation between higher level athletes and lower level athletes despite similar training. Really, we dive into all of the variations of weekly HRV CV and what they mean for your training and competition prep. We cover a lot. We even cover how coaches and teams should implement heart rate variability monitoring, differences in HRV changes from aerobic and anaerobic training, the difference between minimum effective dose and maximum effective dose, how to avoid parasympathetic saturation and why to measure HRV in a seated position. Real quick, last one is how to use HRV to determine when a stimulus is no longer sufficient for adaptation. So we really cover a lot. Andrew has got a wealth of knowledge. And let’s go ahead and dive in.
Welcome to the show, Andrew. We’re excited to have you and appreciate you taking the time from your busy schedule to share your knowledge with our audience. Since we have a lot of great topics to cover, why don’t we go ahead and kick it off? Even though folks have probably heard of you, why don’t we start with a little bit about yourself and your background?
Andrew Flatt: Yeah, I’m currently working on my Ph.D. at the University of Alabama in exercise physiology. My research interest obviously pertains to heart rate variability monitoring in athletes. Athletically I grew up playing hockey, played rugby, and eventually stuck with football, played collegiate football. Once I finished playing football, I gravitated towards power lifting and now I’m a very recreational power lifter. I don’t compete nearly as often as I’d like to. Maybe I’ll pick that up again in the future.
I got my Master’s Degree in Exercise Science with a concentration in performance enhancement and injury prevention. I have a background in strength and conditioning, but more recently I’ve gravitated more towards the sports science side of things in terms of less in the trenches in terms of spotting and counting reps and so forth and more on the side of the monitoring, collecting data, analyzing and providing reports to coaches and how that can influence training loads and so forth. So that’s kind of where I am at currently.
Jason: Nice. Thanks for sharing all that with us. For those that don’t know, Andrew had the opportunity to dig through tons of HRV data from collegiate and professional sports teams to recreational fitness and sedentary populations. So one of the topics I wanted to take a deep dive into are the differences between elite and recreational athletes. So before we dive into all the details, let’s get a big picture view, what are the high level differences between elite and recreational athletes?
Andrew: All right. So I think any informed individual who has been monitoring HRV in athletes for any given period of time can actually probably look at the HRV trend of a high level athlete versus a low level athlete and distinguish purely based on what the data looks like if you were to plot it on a line graph for example.
There’s a couple of reasons for that, but the main differences are higher fit athletes and more experienced athletes, athletes with a greater training history, they’re going to tend to have a higher HRV. Specifically, I’m talking about a parameter called the RMSSD, the root mean square of successive R to R interval differences. It’s a parasympathetic marker. So their HRV is going to tend to be higher and they’re going to see less fluctuation on a day-to-day basis. Whereas a lower fit athlete or a less experienced athlete, they may have lower HRV and they’re going to experience greater day-to-day fluctuation in terms of their score. So they can see 10 to 15-point changes on any given day.
A lot of that has to do with fitness level. In fact, in the research level that we’ve done where we’ve looked at the mean and the CV, the CV represents the daily variation in sports that I was just talking about. There’s a very strong relationship between these parameters and fitness. The higher fit you are, the higher your score is and the less fluctuation you have, and the lower fit athletes are going to have lower scores and more day-to-day variations. So what that tells us is that the higher fit athletes, we already know this, but they have a greater ability to handle higher and more frequent training loads because of their fitness level. They have adapted to a certain amount of training. And therefore, they’re not going to be stressed or fatigued from it on a day-to-day basis, whereas a lower fit athlete, you put them into the same workout with your higher fit athletes and you’re going to see much bigger changes in their scores because of it.
So right off the bat, your higher level athletes are going to tend to have higher scores and less day-to-day fluctuation. And your lower fit athletes are going to tend to have lower scores and more day-to-day variation. That’s a general overview. Each athlete is going to be a little bit unique, but in terms of generally speaking, that’s what we kind of see.
Jason: So we know that elite athletes are more resilient to the stress of training, and what you’re saying is that that shows up pretty obviously in their HRV data as well.
Andrew: Absolutely. I would even take that one step further and say they’re more resilient to the specific type of training that they’re doing. You take an endurance athlete who has primarily been training a certain way and you introduce a novel training stimulus to them, then you will start to see bigger fluctuation on their scores because they’re not adapted to that type of training. Now just being more aerobically fit, maybe they can probably handle it better than someone who is less fit. But I would say there’s specificity to the type of training because we will see in very high fit athletes, when we change training up, we will start to see the fluctuation in their scores, which is indicating that this is a stimulus, it is provoking a stress response, and they do recover from that after a day or two and so forth.
Jason: A trend that I’ve noticed especially in endurance athletes or athletes that do a lot of repetitive exercise is that they often end up training at fairly high volumes even at the recreational levels, and they’ll often say things like, “I just can’t get my HRV to drop or change much at all.” The first thing I think is that to get the best results, they should definitely be working with an experienced coach or trainer who can monitor their data and adjust load and volume and intensity appropriately. But the second thing that comes to mind is that they should consider introducing a different stimulus and see what happens. In your experience, would you say that a higher volume recreational athlete might see the same trend that we were just talking about if they were to introduce a different stimulus such as a different movement pattern or changing up intensity or type of training?
Andrew: Yes. I think your HRV is going to respond to the stimulus. If you’re unadapted or you’re unaccustomed to that type of training, you will see a decrease in your score. You will probably be experiencing more fatigue and more soreness. I mean, first of all aerobic training, long, steady, safe type training, that actually tends to have a stimulatory effect on HRV, which is one of the reasons why it’s recommended as an effective recovery tool. 15 to 30 minutes on a bike or an Airdyne or a light jog can actually enhance recovery or increase cardiac autonomic activity.
Whereas anaerobic type training so intervals, increasing intensity and volume and resistance training, that is going to actually tend to decrease HRV and may require a little bit more recovery time and so forth, which may be effective to include aerobic type training as a recovery and modality for those type of athletes during certain times of the year where you do need to really enhance recovery because of time constraints or because of frequent competitions and so forth.
Jason: That leads us to another difference between elite and recreational athletes which are the different time and schedule constraints that they deal with. Could you talk a little bit about that?
Andrew: Yeah. If you’re an elite athlete or a high level athlete, you are basically at the mercy of your schedule. You have a competitive season, you have a preparatory period and so forth, and there’s not much you can do about that. So you may only have eight weeks to prepare for the season, and so your loads are going to be a little bit more concentrated. You may be training more frequently with higher intensity. I mean we see it pretty regularly in most team sports with pretty seasoned training camp for example where two-to-three week periods of sometimes three-a-day practices. Generally three-a-days won’t happen every day but that’s a high level of training and it’s an abrupt increase where typically athletes aren’t preparing for training camp by training three times a day. So I think monitoring HRV in these athletes during these times is very important because HRV is going to respond in athletes who are quickly accumulating fatigue and we should heed that warning sign and really ask ourselves do we really want to put this athlete through another three practices today or two practices? How can we facilitate recovery a little bit in this athlete? Because one of the biggest risks of injury is just increase in training loads.
So I think elite athletes definitely would benefit from HRV monitoring, whereas recreational athletes aren’t really limited by competition times or competitive season. So they have the luxury of manipulating training on a daily basis to try and maintain a stable HRV trend which currently is still theoretically superior. But we need more research to show should we train to maintain an increased HRV? Is that superior or not? We still need more research especially in different kind of athletes, strength training athletes, sprinters, and so forth. But your training schedule is definitely going to limit you if you’re a competitive athlete; and therefore, HRV is probably going to be a very good tool for helping you plan and adjust training accordingly.
Jason: Let’s talk training load. The term minimum effective dose gets tossed around with regard to training and many people are keen on finding the minimum effective dose especially recreational athletes or health seekers. On the other hand, elite athletes or competition-focused individuals might be seeking the maximum effective dose. Kind of two sides of the same coin, so to speak. Is HRV a tool, a useful tool, in both of those scenarios?
Andrew: That’s a loaded question for a number of reasons. I guess because adaptation in an athlete that enhances performance could come from various qualities in terms of increase in the fitness of an athlete can technically transfer to better performance on the field because they can withstand more high-intensity runs and changes of direction. Therefore, they can play longer at a higher intensity so that technically should enhance performance, strength as a quality, power as a quality also. That can technically transfer over to increased performance for a sport. But what about strategic skill acquisition and becoming better at changing direction? So I guess what I’m trying to say is HRV is going to respond to stress, whether that’s training or sleep quality or whatnot, and that would be important definitely for managing training load to guide training and so forth.
But we can see improvements in performance without changes in fitness and strength and so forth. So it’s hard to say that HRV conclusively can be used for that reason. But I think in terms of especially physical qualities, HRV may be useful for kind of observing when a stimulus is no longer provoking any kind of stress response and adaptation to it. That’s what we saw in our female soccer players that at week one, we saw in most of these athletes a large degree of fluctuation in their scores. And then at week three, those who were showing less fluctuation in their scores were the ones that went on to have the higher level of fitness, whereas girls that saw an increase in their daily fluctuation were the ones that ended up showing smallest the improvements or even regress in their performance.
So I think performance is a whole another parameter that we need to be able to monitor. Again, I don’t think it’s as black and white as we’d like it to be. Can it be useful? Absolutely. But I wouldn’t say it’s the only thing you want to be monitoring for assessing that. What are your thoughts?
Jason: I liked that you mentioned that it’s not black and white. Often trainees might think, “Well, should I work out more or less?” Often, there is a definitive answer to that. But sometimes the answer might even be neither. Perhaps the fitness level of that athlete is pretty good but it’s actually skill development that is the main area that needs improvement. So it’s important to keep the context of goals in mind. That leads to another difference between elite and recreational athletes. But before I jump into that, you’ve mentioned the term parasympathetic saturation before in our discussions. Could you tell us a little bit more about what that is?
Andrew: Right. I guess I’ll preface this by saying that this is not frequently seen, at least in terms of my experience. Parasympathetic saturation tends to occur predominantly in very high level endurance athletes or individuals who are undergoing very high volumes of endurance training.
Parasympathetic saturation, the results of would be having decreased heart rate variability despite having a very low resting heart rate, which is counterintuitive because typically, the lower your resting heart rate, the higher your heart rate variability is. There tends to be an inverse relationship there. But what’s happening kind of physiologically is that the acetylcholine receptors on the heart that respond to vagal stimulation, the vagus nerve is going to release acetylcholine which will bind to the muscarinic cholinergic receptors on the heart, and that tends to slow heart rate down. With respiration, we tend to get kind of this natural arrhythmia and heart rate where when we breathe in, it speeds up a little bit, and when we breathe out or when we expire, it slows down.
But when we have saturation of these acetylcholine receptors, we tend to lose that variability. So we tend to lose that respiratory sinus arrhythmia so heart rate remains relatively constant. More like in a metronome despite it being very low. This has been reported in high level ultra marathoners and so forth that you’re more susceptible to it in the supine position simply because you’re in a more rested or relaxed state where our heart is not being challenged to overcome gravity, to pump blood upwards and so forth. So I would say for the recreational athlete, that’s probably not a concern. But for the high level, elite endurance athletes, it may be something that they want to consider. Measuring in a seated position or even standing, I would always recommend for higher fit athletes. For most people I recommend measuring HRV seated. But if you’re an extremely fit athlete with a very low resting heart rate, I would just measure standing up. Hopefully that should take care of any issues of parasympathetic saturation.
Jason: Cool. A question I often get is my heart rate is this or my heart rate is that. Should I change the position that I take my reading in?
This often comes from users who have extremely low resting heart rates, sometimes even in the low 40s when sitting straight up without back support. So in extreme cases, I recommend that they stand for their readings. But in most cases, as long as there isn’t excessive discomfort, I recommend sitting for pretty much everyone.
Now, a quick word about our sponsor, HRVcourse.com. If you’re looking to take your usage of heart rate variability to the next level, check out the educational video courses over at HRVcourse.com. I’m one of the contributing instructors and so are some of the experts you’ve heard on this podcast. Don’t forget, listeners of this podcast get a 10% discount on your first course using discount code ELITEPODCAST. Courses are only open for enrolment at certain times of the year so check it out today at HRVcourse.com.
Just to catch everyone up who’s listening, we have just fast forwarded a few months to the second part of this interview. My internet connection in Thailand made the first part a bit painful to record so we decided to continue once I got back to the States. Thanks again for joining us, Andrew. Let’s kick this part of the discussion off with some coefficient of variation or HRV CV. This may be one of the topics that we get asked the most about from coaches, sport scientists, and high level athletes so it should be pretty interesting.
HRV CV has been a part of our team dash for some time and we talk about it in the foundations course over at HRVcourse.com. But it was really your research, Andrew, and your experience that helped put CV on people’s radars on the first place. And you’ve also recently mentioned that your thoughts have evolved a little bit about it. So let’s dive into that a little bit. First, what is the coefficient of variation of heart rate variability and what is it used for?
Andrew: The coefficient of variation is really a measure of reliability. So the way we’ve been using it is across a one-week period where you record HRV on a daily basis and calculate the weekly mean, and that’s just the average of your seven scores. And then you can calculate the standard deviation. When you divide that by the mean and multiply it by 100, that’s your coefficient of variation. It’s basically telling us how much your scores fluctuated throughout the week. For example, if you had a really big decrease in HRV at some point of the week, then your coefficient of variation is going to be higher.
It also will increase your coefficient of variation if you had a big spike in HRV. So it doesn’t discriminate between whether if you’re seeing higher score or lower score. It doesn’t tell you exactly what’s happening. It’s just telling you that there’s more fluctuation or less fluctuation.
Starting in 2015, we started working with the Alabama swim team. Originally it started with just the sprinters, which was very interesting to me because there hasn’t been a lot of research published in sprint athletes or anaerobic athletes. It’s predominantly been in endurance athletes and for good reason. But we ended up with at least one month of data from over 30 swimmers. That included sprinters and non-sprinters but no extreme endurance athletes. They were all pretty short-distance swimmers. I divided them based on their training status. This is unpublished data. We’ve accumulated so much data the last couple of years that we just haven’t had time to sit down and record it so I look forward to this summer once class is done and we can finally write it up.
But actually, what we found was the national and international level competitors, and some of these are athletes preparing and competing for the Olympics, their coefficient of variation was significantly lower than the conference level competitors. We also saw that the international level competitors have a higher average HRV. This is based on one month of data. At the same time, when they’re all pretty much participating in the same structured training. So there’s a baseline difference in higher level athletes. I guess it was kind of unique insight at first, but then I started thinking about the previous literature.
Dr. Jamie Stanley had a great meta-analysis paper where he was looking at parasympathetic reactivation after exercise. He found that higher level athletes showed greater and faster recovery after training sessions. So if you think how that would apply across the week with the coefficient of variation, if you’re doing a hard training session and you’re recovering faster, you’re not going to see big swings in your HRV scores on a day-to-day basis.
There’s a study by Dr. Daniel Plews in very high level, in Olympic level rowers. What he was finding was that after high intensity training sessions above the second lactate threshold that the rowers that ended up winning medals were showing much faster parasympathetic reactivation recovery after those training sessions, whereas non-medaling rowers were showing delayed recovery. So their HRV scores the next day were lower compared to the medaling athletes.
Then the same group, Daniel Plews, Martin Buchheit, I think Yann Le Meur was on that paper as well, they looked that if you can calculate the weekly average of your HRV, in only three days essentially, they were looking at what was the minimum amount of days that we needed to record HRV to acquire a weekly mean because for compliance issues, if you don’t measure HRV every day, it’s not a problem. They had elite level endurance athletes and then they had recreational endurance athletes. What they found was in the elite level athletes, they can acquire a weekly mean in three days, randomly selected from a week, whereas in the lower level athletes, the recreational athletes, you needed at least five days to capture a weekly mean value.
Why would that be? That just tells us that in the elite athletes, they’re experiencing much less day-to-day variation. Therefore, you can capture the weekly mean in only three days, whereas the lower level athletes, they’re showing much bigger swings. They’re increasing and decreasing in a day-to-day basis. The CV coefficient of variation is higher and therefore it can’t be captured in fewer days across the week.
That’s kind of the basis for making sense of the coefficient of variation. Higher level athletes at baseline are going to have a smaller coefficient of variation. They just handle training better. They’re recovering faster and so forth. They’re more accustomed to the loads, probably has to do with fitness level. We don’t have yet, that I’m aware of, a fitness test on all the swimmers that we did, that the coaches might have something that we’re going to have to look into. But I would assume if we were to test the fitness on all those swimmers, there would be a strong correlation between the CV and fitness level. The higher level international competitors probably are higher fit which explains some of the variants and their coefficient of variation of why it’s smaller.
And then in a recent paper that we have in review in collaboration with Dr. Fabio Nakamura, he collected HRV data in elite rugby players across a five-week pre-season period. One of the findings we reported was the relationship between the weekly mean and the coefficient of variation for each athlete, and we found a significant relationship. At first I thought, this is obvious right? Then I thought maybe it’s not so obvious, that just because you have higher HRV, you have less day-to-day fluctuation. So I started to look at all of our compiled data from two different soccer teams, from swimmers, cross-country athletes, and football players. Just within the teams themselves, I was looking at relationships between the mean and the CV. Sure enough I’m consistently finding significant relationships, which is telling us that the higher your HRV is, the less day-to-day fluctuation you’re likely going to have. Now the correlations range from moderate to large. So it doesn’t explain all the variants. It doesn’t mean that just because you have HRV, you’re going to have less, a smaller CV, but most of the time you will. That appears to be the case.
So you start to ask yourself, “Should we purposely try and increase our HRV so that we have less day-to-day variation? Is that meaningful at all?” I think that you got to dip into some other research in terms of how one handles stress based on your HRV. There’s been some really interesting research, kind of psycho-physiological research where they’re looking at baseline heart rate variability, then they give them some kind of like a Strub test or some kind of stressful event.
In the post stress period, they’re measuring heart rate variability again in addition to blood pressure, cortisol, inflammatory markers like tumor necrosis factor alpha and so forth. Essentially what they find is, and there’s a nice study in the European Journal of Applied Physiology and I can provide the link later. I just can’t remember the author. I think Julian Thayer of Ohio State was on that one.
Essentially, what they found was that the individuals with higher vagal activity, higher parasympathetic markers of HRV, they respond to the stressor better. They get less of a reduction in HRV. They get a smaller stress response in terms of cortisol and inflammatory markers, and then those markers returned to baseline much quicker than individuals with lower HRV. So the question is can we purposely increase our HRV? And one of the easiest ways to do that is through aerobic exercise. This is very well-established that if you increase your fitness, aerobic fitness, HRV is going to go up. It happens time and time again.
So if we can increase our HRV, our parasympathetic related HRV, will that allow us to handle and adapt to stressors better? And there has been research where they essentially put people on a fitness program, look at their markers of HRV and then see how they respond to the stressor. Time and time again, and again, I’m drawing blanks on the names of some of these authors, they tend to respond and recover faster the more fit people and those with higher HRV.
So going back to our research, what we found, you kind of asked about changes in fitness and the coefficient of variation, during week one of the training program, we got their heart rate variability values every day to see how they responded to the first week. So a new stimulus, they had just come off a couple of weeks of a break so the first week was even though the training loads weren’t super high, it was stressful for them because they were a little bit detrained. These were female soccer players, collegiate soccer players, so not all of them necessarily had a giant or a big history of resistance training and all that kind of stuff. We knew it was going to be physiologically stressful for a bunch of these athletes.
What we saw during week one was pretty high coefficient of variations across the week. But we wanted to see by week three if the change in the coefficient of variation as well as the weekly mean of HRV predicted or related to eventual changes in fitness based on their Yo-Yo Intermittent Recovery test values. We got those at baseline and we measured them again at week five. What we found was athletes by week three who saw a reduction in the coefficient of variation ended up being the ones that improved the most in their fitness test.
I should also add that we also found a significant relationship between the weekly mean, sorry it was non-significant because our sample size was only 12 subjects, but qualitatively, it was a large correlation. It was a 0.5 correlation indicating that the increase in your HRV, so your increase in the weekly mean in addition to a reduction in the coefficient of variation was a positive response to the training. I think that’s an important distinction because if you a see a decrease in your HRV, weekly mean in addition to a decrease in your coefficient of variation, that could be indicating something entirely different.
So just looking at changes in the CV alone isn’t going to tell you everything. You kind of want to see how the weekly mean changes along with the CV, as a reduction in the weekly mean in addition to a reduction in the CV is probably indicating pretty high fatigue because their HRV is dropping and it’s not coming back up to baseline. It’s chronically suppressed. So that could be indicating fatigue. Whereas if the HRV is increasing and there’s less fluctuation, most of the time that’s probably going to indicate that they’re handling training stress well. Again, there’s always exceptions to that too because increases in HRV have been related to non-functional overreaching in elite endurance athletes. We’re talking about team sport athletes here and not so much the triathletes. That’s not really in the context of this discussion.
Jason: So we talked about how you definitely have to look at both the mean and the CV and that the mean can give insight into how much of a change in CV you might expect to see. So if you look at two individuals, one with a lower average HRV and one with a higher average HRV, then given a similar stimulus, you can usually expect a higher coefficient of variation or change in HRV for the person with lower average HRV?
Andrew: Especially because both the mean and the CV tend to relate well with fitness, whether it’s VO2 max or max aerobic speed. Individuals with higher HRV tend to be the most fit. We’re also seeing a very similar relationship with the CV. The lower the CV, the higher the fitness. So I’ll just throw that in there as well.
Jason: That explains why my CV is so high sometimes. So do you typically focus solely on the weekly mean and weekly coefficient of variation? Or do you also look at monthly or longer terms?
Andrew: Yeah, you definitely can look if you want to see longitudinally how that looks over four weeks or whatever. But typically I’m looking at seven-day values. If the athletes are participating in a sport that the weekly structure is pretty much the same so they compete on the same days, they practice on the same days, then I like to see the week-to-week changes in the mean and CV. I’m also looking at acute daily changes too because though I don’t like to be hypersensitive to them, very large increases and decreases are usually indicative that sums up. A lot of my research has been very observational, where we’re not intervening because we’re just trying to validate that these trends that we’re seeing are either leading to good things or leading to bad things. And when working with a new coach, I always suggest, listen, it makes sense why we’re going to start recording and looking at recovery status but just so we could kind of validate it on our athletes, let’s just observe how they respond to training and then we’re going to analyze things, who underperforms, who performs well, who gets sick, and all these stuff. We’ll see what the HRV trend is telling us. Most coaches I’ve worked with end up wanting to continue monitoring HRV just because they can see some of these trends. So on a week-to-week basis, the structure is relatively similar, but I also look at the rolling seven-day average.
To be honest, when I’m working with a team, just to provide insight to the coach, I’m generally not doing a ton of data analysis. I’m just observing the trend. If it’s visualized nicely, I can see when there’s more fluctuation. I could see when the mean is going up and when it’s doing down. So it can be interpreted relatively quickly when you know what you’re looking for. But monthly changes can tell you kind of just if you’re doing an aerobic block of training, for example, or an anaerobic block of training, those are very vague in general, but I would expect the HRV to respond differently. During aerobic training, I would expect to see increase in HRV and probably decrease in the CV, whereas if you’re doing primarily high intensity training, I’m going to expect that by 24 hours, by the next day when you measure your HRV, it’s not necessarily going to be up baseline. There’s going to be a lot more fluctuation. Because of that, your mean’s going to go down usually. So you can kind of just see how they respond across the month.
Jason: In our discussions, you mentioned that 7% was a useful threshold for weekly coefficient of variation. So for athletes, if your weekly HRV CV is above 7%, that would be considered a higher CV. So let’s run through the list of weekly mean HRV and weekly HRV CV starting with what does it mean if weekly HRV is low and weekly HRV CV is high?
Andrew: If I have no indication of what the training is looking like, my prediction or my guess would be they’re either starting a new training phase or a new program where the stimulus is somewhat novel and they’re stimulated by it. So the CV is going to increase and the mean can decrease as a result of training load. I’ve seen this in several different teams of different sports. With decreased training load across the group, the CV tends to go up and the mean tends to go down. The CV may be a little bit more sensitive because it’s more sensitive to change. Sorry, it’s more subject to change. The mean might go up or down a couple of points but the CV can increase in the most fit. What I’ve also seen is in very fit athletes who are very well accustomed to a given training stimulus and they see a decrease in their mean and an increase in their CV, almost always we can attribute it to some kind of non-training-related stressor.
It could just be academic stress. It could be something is going on with their family. Someone passed away and they were dealing with that. In your high level athletes who you would expect to handle this kind of training, well, when they show a decrease in the mean and an increase in the CV, I would look into the non-training factors that can be attributing to that. That is important because you’ll be surprised how quick that can run them down. Despite it not being training-related stress, it really does compromise their ability to tolerate and recover from it. I would say in high level athletes, when you see those changes. I’d be more concerned about that. I would expect to see in your lower level athletes. But when you start to see them in your higher level athletes, pay attention to that and be mindful of it.
Jason: So if you were coming off of a period of rest or an off-season, you might expect a decrease in weekly mean HRV and an increase in weekly HRV CV. But if you aren’t expecting this type of reaction then it may be concerning especially for more high fit athletes.
Andrew: Yeah. And again, I’m not saying you have to throw up a whole bunch of red flags and change everything and take them out of training. You know what I mean? That’s not at all what I’m saying. I’m just telling you that it’s reflecting some physiological stress. Depending on your situation, what training phase you’re in, be mindful of it. Are you trying to accumulate fatigue and stress? Obviously non-training stress, we’re never trying to accumulate. We only want to manage that as best as we can. But if we continue to increase training loads and neglect or not pay attention to these non-training factors, we can be putting that athlete at risk of overdoing it a little because they’re just not going to respond to training nearly as well.
Jason: Is there any difference if weekly mean HRV just is the same but CV increases? And does that happen often?
Andrew: Yeah, because if the increases and decreases are similar, that the average stays the same. You know what I mean? You can have a week where your CV is really small and then next week your CV increases substantially, but your mean can stay the same. So absolutely, that can happen. I would say that, and this is hypothetical, that we can maybe interpret if the CV increased but the mean didn’t really change, then I would say that that’s a very moderate level of a stimulus. I use the word fatigue a lot, but we got to be careful with how we’re defining fatigue. In the research world, there could be a lot of people saying, “How do you know that’s what he needs?”
All I’m saying is that there’s some kind of physiological stressor that’s causing these day-to-day changes that are outside of their baseline because when you’re looking at during normal training how someone responses normally, you’re going to get an idea of how they typically respond. When the respond changes, whether there’s much greater variation or much less fluctuation, that’s pretty meaningful use of this. You can see that not much of a change in the mean but the CV can increase. I would expect to see that with any kind of change in training or an increase in loads. That would almost be the earliest stage or kind of one of our earlier signs that they’re stimulated. And then the one that we previously talked about was a decrease in the mean with an increase in the CV. I would suggest that especially in team-sport type athletes that would be the next step of where fatigue would be increased a little bit more or there’s more physiological stress taking place because that tells us that the fluctuation is downward because the mean is going down. So we can almost kind of categorize that as very moderate a little bit more and then more severe fatigue comes next, which we can get into.
Jason: Right. My experience with this pattern for folks that are training for some type of sport is that they are getting some type of stimulus, but they’re also recovering back to their average levels of HRV. So they may not be increasing aerobic fitness, but they may see improvement in strength and skill or some other performance marker because they’re likely getting some sort of stimulus and also recovering back to baseline at least.
Andrew: Yeah, and we can only increase our HRV so much. Obviously the higher your baseline HRV, even just genetically some people are going to have higher HRV. You can only get it so high.
Jason: Right. The last scenario is weekly mean HRV increasing and HRV CV increasing also. Both are going up. So what would that indicate?
Andrew: The scores are scattering a little bit so you are probably in the early stages of some type of training program that you’re adapting reasonably well to because your overall trend is starting to increase. But there’s still obviously some kind of perturbation taking place. It might take a day or two for your score to return back to baseline, but it can exceed baseline substantially where we see we just got a spike in HRV here and there. I mean, there are plausible explanations with changes in plasma volume that may account for these spikes in HRV after a couple of days. But with an increase in HRV and an increase in the CV, I really need to look at training loads and see, and then some wellness questions just to kind of see what’s going on and what we can really attribute that to. But I personally wouldn’t be alarmed by that kind of trend in terms of we got to look into making some type of intervention here.
Jason: Okay, great. This is fantastic information. We’ve got one more variation to cover in this episode of HRV, mean, and CV before we break for a second round. But by the way, Andrew is sharing a written breakdown of these CV variations with us that we’re posting on the Elite HRV website. We’re going to announce on Facebook and Twitter and all that when that’s posted. But keep an eye out on Elite HRV blog because it may already be up when you’re listening to this. Now let’s look at HRV increasing and CV going down like you might see in a taper situation for example.
Andrew: Generally that’s going to happen during a reduction in training loads so that could be a taper. It could just be one from a high level week to a relatively lower level week. In my experience, a good response indicates that you’re handling and recovering well. You’re experiencing much less day-to-day fluctuation. Your score trend may be increasing a little bit. Almost always in my experience, that’s indicative of a good positive response. Training adaptation is good and this was from just from one case I did in cross-country endurance athletes, but we found 0.92 correlation between weekly eight kilometer race times and a coefficient of variation where when there’s less day-to-day fluctuation across the week, he performed better every single time essentially.
In my experience, that is almost always indicative of a good positive response and possibly a higher readiness to perform just because you have not been encountering major stressors, or if you were you would just handling and adapting to them really well. You might be good to go. And we did see that in a bunch of sprint swimmers. We were monitoring through the whole season, but particularly the particular block that we were looking at was in preparation for the FCC championships. We looked at the mean and CV during the week of baseline and then during a two-week anaerobic overload and then during a two-week taper. We’re just looking at the mean and CV changes.
That change in the mean and the CV, there was an increase in the mean, a decrease in the CV leading right up in the competition. The athletes that demonstrated that, which was most of them, all performed really well. And then there were some athletes that underperformed and their trend was not showing that. So for those reasons, that’s kind of why I usually attribute that to positive response and good adaptation.
Jason: I’ve also seen the opposite pattern in higher level endurance athletes. Often with elite marathon runners or triathletes that their HRV will actually increase throughout a training period and then both HRV and CV will drop in the taper. Have you seen that as well and how was that different?
Andrew: That’s actually not uncommon for endurance athletes. A bell-shaped trend in HRV has been reported before. I especially think Daniel Plews in some of this previous work showed that several weeks out from competition, you’re seeing an increase in the HRV which sometimes can be associated with nonfunctional overreaching and this was found in Yann Le Meur’s paper, in Med Sci, I think it was 2013. But they found parasympathetic hyperactivity during overload training was associated with reduced endurance performance markers.
But when you reduce training loads, that parasympathetic hyperactivity that you’re seeing starts to return back to baseline. So if you’re looking at the trend, as you’re increasing training loads, specifically with endurance training, you could see an increase in HRV which may not be a good thing. This might be confusing to everyone because we’re just talking about how it’s usually a good thing. This is specific for endurance athletes, high level endurance athletes.
And then as they reduce training loads, it comes back down to baseline and that’s been associated with freshness and recovery and ready to perform. So you absolutely have to take your training context of what sport you’re doing, what activities you’re doing. And the nature of your taper, I mean endurance is a broad category. Are we talking triathlete, marathon? Are we talking 5K? So even that requires some context because depending on if you build up your training with a lot of endurance, aerobic training, we could actually see an increase in your mean just because of the effective aerobic training on parasympathetic activity. But then if your last week or last couple of weeks of the taper, you start to cut out aerobic a little bit and focus on more high intensity training, we know that that actually tends to cause acute decreases in your HRV and it might take a day or two to return back to baseline. So your average is actually going to go back down so we could see a bell-shaped trend in that regard as well, which is not necessarily associated with parasympathetic hyperactivity due to overreaching but just because of the content of aerobic training, and then switching gears to high intensity training which tends to cause a decrease in HRV. So it can be very confusing and requires context.
Jason: Folks, that is only half a discussion with Andrew Flatt. The next episode of the podcast is another deep dive with Andrew on completely new topics regarding HRV and sport performance. There’s also one more combination of CV and HRV to cover. We also discuss injury potential in HRV, sympathetic activation for better performance, hydration and plasma volume, the three-step process for implementing HRV and when not to use HRV.
As you can see, Andrew lives and breathes HRV for sport performance. If you want a more in-depth understanding of the mechanisms behind HRV and how to apply them, don’t forget to check out HRVcourse.com and use discount code ELITEPODCAST at the checkout. And to hear round two with Andrew and to get more information like this episode, definitely subscribe to the show on iTunes or your favorite podcast app. Also, the best way to help us continue to bring in more experts is to leave a review on iTunes. Simply go to eliteHRV.com/iTunes and stick a short review there please. We read every single one of them and it helps a lot. Appreciate your time and see you next time.