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Blog post by Marco Altini Last week I had the opportunity to chat with Jason Koop and Corrine Malcom about heart rate variability (HRV), "readiness" scores, resting physiology, and wearables, in the context of training If you are interested in understanding the nuances of these aspects, including their strengths and limitations, this episode is a good starting point Don't fall for cults or for those who trivialize everything that is human physiology. Instead, strive to understand these aspects, and you'll be a better athlete or coach Thanks again for having me!  Blog post by Marco Altini In the second part of our latest paper, we analyzed individual stress responses to:
Using 1 year of data per person, for 28 000 people. This is in my view the most interesting part of the paper Why?  This type of analysis allows us to answer important questions: Can a morning measurement capture individual stress responses effectively? Is it worth the trouble to look at HRV, or is HR enough? What is the difference between the two, when it comes to stress responses? Data collectionMeasurements and annotations (training intensities, sickness, etc.) were collected using HRV4Training, first thing in the morning Most measurements were taken with the phone camera (validation here). Let's quickly look at our analysis framework first. How do we analyze individual stress responses? For each person, any given day there will be many stressors. However, if we take hundreds of days of data per person, and look at one stressor at a time, we can isolate the stressor and better understand its impact on resting physiology.  What did we learn?Training intensityBelow are the results for training intensity (low vs high-intensity days). The change in HRV is 4.6% while for heart rate is 1.3% (with respect to a person's average). HRV is therefore more sensitive to this stressor. The change in HRV does not reduce across age groups, indicating how HRV captures training stress equally well for older individuals, while the change in HR reduces. Additionally, women tend to have a less marked response (more about this later)  We also split the annotated intensity into four categories, as shown below. Once again we can see how HRV is more sensitive to changes in training intensity, but also how these measurements capture very well self-reported training intensities:  Menstrual cycleThe change in heart rate was 1.6% between the follicular and the luteal phases, while the change in HRV was 3.2%. Once again, HRV is more sensitive. These differences might also be the reason why other stressors show somewhat less marked responses in women.  Alcohol intakeChanges in alcohol intake are 3-4 times larger than changes due to training or the menstrual cycle (6% change in heart rate and 12% change in HRV).  SicknessNot surprisingly, sickness is also a very strong stressor, similarly to alcohol intake (6% change in heart rate and 10% change in HRV).  What are the implications?When using HRV for training guidance, lifestyle is key, and poor lifestyle or health issues will take over. A holistic approach to health and performance is needed. Strength of the stressorTo recap, changes due to training intensity and the menstrual cycle are typically 3-4 times smaller than changes due to sickness or alcohol intake. Changes in HRV are 2-4 times larger than changes in heart rate in response to the same stressors. InterpretabilityWhen we contextualize the percentage changes reported in this paper with what we know from literature, e.g. that the smallest practical or meaningful change in heart rate is 2% and in HRV is 3%, we can see how changes in heart rate are below this threshold, and therefore smaller than normal day to day variability.
This means that heart rate is not sensitive enough unless we have very strong stressors (e.g. alcohol intake or sickness). This also means that while HRV is more sensitive, it is also less specific, as shown by the typically smaller effect sizes. In other words: changes in heart rate are often of no practical utility (smaller than daily variability). On the other hand, higher stress will be reflected on HRV data no matter where it comes from and it might be difficult to get to the source (context is key). We speculate that these findings might lead to new forms of HRV-guided training, where rest days are prescribed based on large changes in HR (as these capture only very strong stressors), while training intensity is modulated based on more subtle HRV responses. You can find the full text of the paper, here. Thank you for reading Blog post by Marco Altini In our recent publication, we analyzed the relationship between heart rate and HRV with respect to individual characteristics such as:
In a large sample of 28 000 individuals. What did we learn? Some of the findings are larger-scale replications of what we knew already Consistent results with published literature that used different data collection procedures is a good first step It gives confidence in the quality of the data when we start digging a bit deeper Sex Women have higher resting heart rate than men, but very similar HRV In fact, at a younger age, women have a slightly higher HRV. This is of interest as a higher heart rate would normally be associated with lower HRV. The discrepancy might be due to hormonal differences.  BMI Both underweight and overweight/obese categories show what we have called in the paper a suboptimal physiological profile, meaning that resting heart rate increases and HRV reduces when deviating from the normal range. The strongest deviation is for the obese category.  Age There was no correlation between resting heart rate and age, and a moderate correlation between HRV and age. This is one of the most interesting relationships, as heart rate and HRV clearly decouple and are representative of different processes (more on this later).  Physical activity level The association between physical activity level and resting physiology is stronger for heart rate (r = 0.30, moderate effect size) than for HRV (r = 0.21, small effect size). When we break this down by age group, things get even more interesting. The correlation between physical activity level and HRV reduces by age, getting to r = 0.13 for older individuals. Only for very young individuals (20-30 age group) there is a decent association between fitness and HRV.  Finally, we built models to determine how much variance age, sex, BMI and physical activity level could explain. Are they sufficient to get a good understanding of inter-individual differences? Not really, as they explain 19% of the variance in heart rate and only 15% in HRV.
What are the implications of these findings? A low HRV in aging individuals might be associated with a deterioration of regulatory mechanisms. The weak link between physical activity and HRV as we age might similarly be associated with reduced baroreceptor sensitivity. On the contrary, increased stroke volume due to high levels of physical activity maintain resting heart rate low even for older age groups. In terms of explained variance, it is clear that genetic factors are key in explaining differences in heart rhythm between people. An important implication here is that in our opinion, targeting improvements in HRV as intervention goals might not be realistic, given the strong heritability coupled with reductions with age and low explained variance associated with lifestyle factors such as physical activity level. But there's an important caveat. In this work, we had a large sample. However, this sample is not representative of the whole population, but only of relatively healthy or health-conscious individuals. There might be more to gain for e.g. who never exercises, is overweight, etc. This is why HRV as an absolute value is of little interest (in our opinion). On the other hand, HRV was able to capture day-to-day stressors within individuals with high sensitivity, as I will cover in a future blog. You can find the full text of the paper, here. Thank you for reading! Blog post by Marco Altini Professor Maria Carrasco-Poyatos and co-authors at the University of Almería just published the latest paper on HRV-guided training, titled "Heart rate variability-guided training in professional runners: effects on performance and vagal modulation" Thank you Maria and co-authors for using HRV4Training and for involving me in this work. You can find the paper, here, including the main highlights:
 HRV4Training is looking for brand ambassadors worldwide We believe in empowering individuals with the ability to measure and interpret physiological data so that training and lifestyle stressors can be better balanced, resulting in improved health and performance Learning from athletes and coaches is an invaluable part of the journey, and we are looking forward to getting to know you and your experience Are you passionate about sport and technology and have been using HRV4Training daily at least for 6 months to better balance stress? We are looking for you! What do we offer to the ambassador and mentors?
What do we expect from the ambassadors and mentors?
We are going to select up to 30 brand ambassadors, we accept applications in English, Italian and Spanish. Would you like to spread the word about HRV4Training in another language? Send us a message with your proposal for our consideration! To participate in the selection process, fill in this google form. Deadline is November 30th, 2021  Blog post by Marco Altini Excited to share our latest paper on heart rate and heart rate variability (HRV):
This one has been in the making for a long time, and brings it all together: developing an accurate and affordable method to measure resting physiology, analyzing data at a scale that goes far beyond what we can do in the lab, and as a result, new, valuable insights Give it a read, here  Blog post by Marco Altini You’ve been preparing your race for several months and it’s finally time to taper. Training went really well and you are doing everything right And yet, your heart rate variability (HRV) reduces Learn more about HRV during taper, in my latest blog  Blog post by Marco Altini Heart rate variability (HRV) trends over long periods of time (e.g. from weeks to months) are one of the most interesting and complex aspects to analyze when it comes to resting physiology While day-to-day (or acute) changes reflect well stressors such as training intensity, the menstrual cycle, sickness, alcohol intake, or travel in the day(s) before the measurement, in the long term things are quite different In this post, I will cover our approach to trends analysis in HRV4Training, and cover some of the features in the app that should help you make sense of the data in the longer term Learn more, here  Blog post by Marco Altini  Daily measurements and 7-days moving average for lying down (left) and sitting (right) measurements A few months ago after an interesting chat with an elite team and Andrew Flatt, I started measuring my HRV in the morning while both 1) lying down and 2) sitting. Normally, I have always been measuring while lying down in bed, but Andrew brought up some interesting points which I thought were worth investigating further, at least in my own data. In particular, the reason for doing so, is the following: adding a little stress (e.g. sitting or standing instead of lying down), might better capture your physiological response (or capacity to deal with stress for the day). It's a physiological challenge (more on this later). In terms of the protocol, i would up and measure while lying down in bed, using HRV4Training (phone camera for one minute). At that point, I would sit, and after a few seconds, I'd measure also while sitting (another minute with the camera). Between measurement, the time would be rather short, something like 30 seconds. Let's look at the data. First of all, I'd like to stress how simple measures of agreement might be inadequate, e.g. correlation (often reported) does not tell us anything about deviations from normality.  Correlation between daily measurements (left) and 7-days moving averages (right) for lying down and sitting data While we can have a look at day-to-day correlation and baseline correlations, as shown above, a better way to understand if we are capturing the same information is to use the data the way it should be used for decision making: monitoring deviations from our historical data and normal values (acute drops, etc.). How do we do that? We can use part of the data to compute the normal values (40-60 days), then look at baseline and acute drops. Here both measures show very similar responses: highly suppressed HRV on the same days, baseline reaching the bottom of the normal range the same period, etc. - it is quite clear that both lying down and sitting are capturing the same trends (which would result in the same advice, especially for acute drops and baseline changes, the two key factors in HRV-guided training):  To sum up: in my data, both measures are very similar, especially in the longer term (baseline correlation) as well as in terms of acute drops (single days below the normal range, highlighted in blue in the previous image). What differed? Lying down seems like a squeezed version of sitting. Paraphrasing Andrew, applying a little stress (e.g. sitting) might better uncover the physiological response response, and this in turn, might explain the higher day to day variability when sitting. Note that this doesn't mean HRV will be lower (quite the contrary). Anecdotally I've heard from quite a few people that "when switching to night data, my physiology never changes" (unless sick, or drinking too much, e.g. very large stressors) Do measurements while lying down, and in particular night measurements simply lead to less day-to-day variability or is this associated to the measurement being less responsive to stressors, due to lack of a physiological challenge? In my opinion, both positions are valid and rather similar, as shown by the data here. While some have quite a dogmatic approach ("never measure in this or that position"), it is clear that the same processes are captured. However, there are also differences, and it is important to think it through and consider potential mechanisms and what could be best in an individual case. Most likely, the level of the athlete, baseline HRV (e.g. on the low vs high side of population values), type of sport practiced by the athlete (e.g. endurance or not), as well as other factors such as the application of interest (daily guidance or monitoring long term trends, performance or health oriented) and practical considerations (what modality makes it easier for the athlete to collect daily measurements consistently) should play a role in this decision. One minute of your time might be worth the insights after all. I hope you have found this blog useful, feel free to follow up here on Twitter.  Lying down (left) and sitting (right), including HRV4Training's detected trend
Blog post by Marco Altini How does the body respond to stress? Below I look at heart rate variability (HRV), heart rate, and glucose in response to two very different weeks (N = 1). High vs low stress:
 Some context first Last summer in July I had a strong negative stress response (cumulative stressors), resulting in arrhythmia and concerns for my health I've talked about this before, but here I want to focus on what happened to glucose during that week. Coincidentally, I was wearing a continuous glucose monitor (CGM) since the previous week and noticed that after meals, my glucose was spiking really high, near 200 mg/dL, consistently. Very interesting to see poor regulation at work so clearly.
As usual, I was also monitoring my resting physiology (HRV and HR) using HRV4Training (morning measurements), and saw quite a dip in HRV, as well as a minor change in heart rate This is the type of stress response I often discuss (see for example my guide here).
Physiologically, we know that high stress is associated acutely and chronically with elevated glucose in the bloodstream and reduced parasympathetic activity Pretty neat to see it with simple measurements and currently available technology.
Blog post by Marco Altini
In this interview, we cover:
Thank you Kieran for having me on your channel Blog post by Marco Altini "If you've ever wondered how to tap into the secrets of how that pump in your chest can help you to train faster, harder and longer Marco is just the man to listen to." “We've been using Marco's app for a while to understand how to better regulate training and recovery and in this episode we do a deep dive on the how and why” I’ve really enjoyed talking to ultrarunners Jay and Tris about HRV, thanks for having me! Episode here.  Resting Heart Rate and Heart Rate Variability (HRV): What’s the Difference? — Part 5, takeaways9/30/2021
Blog post by Marco Altini In part 1 of this series, I covered the basic physiology of heart rhythm regulation. In part 2, I discussed the technology required for these measurements, why some sensors can be trusted, and why others can be used just for resting heart rate, and not for HRV. In part 3, we started looking at the data, with an analysis of population-level differences in resting heart rate and HRV. Finally, in part 4 we covered the most interesting aspect: individual-level data. In this final part, I will report the main takeaways of the previous four parts, as a final wrap-up.  “HRV reflects your physiological responses to all stressors, not just training stress,” says Marco Altini, “Tracking HRV allows us to better understand our own response to training and lifestyle stressors, so that we can make meaningful adjustments towards improved health and performance" Thank you Men's Fitness Mag and Kieran for featuring HRV4Training and ŌURA. Find the article, here  Blog post by Marco Altini The past few months have included lots of ups and downs for many of us. Personally, I've experienced some of the worst stressors of the past years, culminating (somewhat ironically) in heart issues, which were fortunately resolved. Below is an overview of my data, showing how morning measurements of heart rate variability can capture very effectively not only the day-to-day acute stressors we are often discussing (a hard training session, the menstrual cycle, alcohol, the acute phase of sickness), but also longer term, or more chronic changes. Don't forget to look at the big picture.  Blog post by Marco Altini We have just released the latest HRV4Training update, adding support for the new generation of iPhone 13. You can find some data of our first tests, here. Enjoy another year of accurate and inexpensive physiological measurements.   Blog post by Marco Altini In part 1 of this series, I covered the basic physiology of heart rhythm regulation. In part 2, I discussed the technology required for these measurements, why some sensors can be trusted, and why others can be used just for resting heart rate, and not for HRV. In part 3, we started looking at the data, with an analysis of population-level differences in resting heart rate and HRV. In this blog, we finally get to the most interesting aspect: individual-level data. Needless to say, both resting heart rate and HRV become a lot more useful when tracked over time within individuals, and this is exactly what I’ll be showing here. I’ll also try to highlight some of the differences between these two parameters, so that you can better understand what the data means when tracked in response to strong acute stressors (e.g. training, sickness, alcohol intake, the menstrual cycle) and in the longer run (e.g. changes in fitness). You can find the blog, here.  Blog post by Marco Altini There is a new heart rate variability (HRV) course out there, put together by Daniel Plews, one of the most prominent scientists in the field. The course is split into two parts, part 1 covering the basics and technology, and part 2, a fantastic resource covering:
Additionally, if you use HRV4Training Pro, you'll see how to use the platform in the context of the points above, as Daniel goes over many examples showing our platform. We highly recommend it, for both individuals trying to get the most out of their data, and coaches using these tools with their athletes. Check out the course here and try HRV4Training Pro for free, here  This week is HRV4Training's 8 years birthday, and we are doing a small giveaway You can win either free access to HRV4Training Pro for one year (more info on the web platform can be found at HRV4T.com) or a t-shirt (either the running singlet or regular t-shirt) To participate in the raffle, simply write a post or blog about HRV4Training either on social media (Instagram, Facebook, Twitter, etc.), or on your blog and send us a screenshot via email at hello@HRV4Training.com or let me know here We are looking forward to learning more about how you use the app and what you find useful. Deadline is next week!  Blog post by Marco Altini In part 1 of this series, I covered the basic physiology of heart rhythm regulation. In part 2, I discussed the technology required for these measurements, why some sensors can be trusted, and why others can be used just for resting heart rate, and not for HRV. In this blog, we finally start looking at the data, and in particular at population-level differences in resting heart rate and HRV, what factors consistently show changes in resting physiology, and what we can derive from this type of analysis. We will discuss absolute values and differences between subgroups of the population with respect to:
Check out the blog, here.  Resting Heart Rate and Heart Rate Variability (HRV): What’s the Difference? — Part 2, The Technology7/22/2021
Blog post by Marco Altini Check out part 2 of our series on differences between Resting Heart Rate and Heart Rate Variability (HRV). In part 1, we covered the physiology, while in this part, we detail important technological differences when measuring heart rate and HRV: ‣ Common technologies (ECG, PPG, BCG), pros and cons ‣ Sensors made for HRV ‣ Managing artifacts ‣ Timing of the measurement ‣ Takeaways Link here  Blog post by Marco Altini I had a nice chat yesterday with Michael @ x3training about heart rate variability (HRV) biofeedback It was my first time trying to cover this topic, I hope you’ll find it useful Episode link here HRV4Biofeedback app here Enjoy  This is a guest blog by Jim House covering the past 2 years of his personal experience using HRV4Training and HRV Logger I have been riding a mountain bike for about 30 years. I am now 62 years old and just retired and have been diagnosed with leukaemia. Rather than sitting around feeling sorry for myself I thought I needed a challenge. I live near Eastbourne in the UK and decided I would ride the South Downs Way, which is 102 miles long (90% off road), including 11000ft of climbing. I have had successes and failures in my training so I have called this blog The Good, The Bad and The Ugly and I hope you can gain something from my experiences.  Jim and his playground The GoodMy approach in the past hasn’t always been very structured, but for this challenge, I decided to do it a bit differently. In early 2020 I started using HRV4Training and got myself a training plan. From the HRV4Training screenshot below you can see just how useful the feedback was to know when to push and when to have a day off, and also the desired effect of adjusting training this way, which resulted in a stable and consistent HRV, never below my optimal range as shown in HRV4Training Pro.  The first 9 months of HRV monitoring showed consistently stable responses as I adjusted my training based on HRV4Training's feedback
Part 1 of our latest series is all about physiology, and in particular goes deep into the differences between resting heart rate and HRV: ‣ Why do we care ‣ Bird’s-eye view ‣ Understanding autonomic control of the heart and more We hope you'll find it useful, enjoy the read  We have ve updated our Ultimate Guide to Heart Rate Variability (HRV): Part 1, that you can find here:
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Marco Altini, founder of HRV4Training Blog Index The Ultimate Guide to HRV 1: Measurement setup 2: Interpreting your data 3: Case studies and practical examples How To 1. Intro to HRV 2. How to use HRV, the basics 3. HRV guided training 4. HRV and training load 5. HRV, strength & power 6. Overview in HRV4Training Pro 7. HRV in team sports HRV Measurements Best Practices 1. Context & Time of the Day 2. Duration 3. Paced breathing 4. Orthostatic Test 5. Slides HRV overview 6. Normal values and historical data 7. HRV features Data Analysis 1a. Acute Changes in HRV (individual level) 1b. Acute Changes in HRV (population level) 1c. Acute Changes in HRV & measurement consistency 1d. Acute Changes in HRV in endurance and power sports 2a. Interpreting HRV Trends 2b. HRV Baseline Trends & CV 3. Tags & Correlations 4. Ectopic beats & motion artifacts 5. HRV4Training Insights 6. HRV4Training & Sports Science 7. HRV & fitness / training load 8. HRV & performance 9. VO2max models 10. Repeated HRV measurements 11. VO2max and performance 12. HR, HRV and performance 13. Training intensity & performance 14. Publication: VO2max & running performance 15. Estimating running performance 16. Coefficient of Variation 17. More on CV and the big picture 18. Case study marathon training 19. Case study injury and lifestyle stress 20. HRV and menstrual cycle 21. Cardiac decoupling 22. FTP, lactate threshold, half and full marathon time estimates 23. Training Monotony Camera & Sensors 1. ECG vs Polar & Mio Alpha 2a. Camera vs Polar 2b. Camera vs Polar iOS10 2c. iPhone 7+ vs Polar 2d. Comparison of PPG sensors 3. Camera measurement guidelines 4. Validation paper 5. Android camera vs Chest strap 6. Scosche Rhythm24 7. Apple Watch 8. CorSense 9. Samsung Galaxy App Features 1. Features and Recovery Points 2. Daily advice 3. HRV4Training insights 4. Sleep tracking 5. Training load analysis 6a. Integration with Strava 6b. Integration with TrainingPeaks 6c. Integration with SportTracks 6d. Integration with Genetrainer 6e. Integration with Apple Health 6f. Integration with Todays Plan 7. Acute HRV changes by sport 8. Remote tags in HRV4T Coach 9. VO2max Estimation 10. Acute stressors analysis 11. Training Polarization 12. Lactate Threshold Estimation 13. Functional Threshold Power(FTP) Estimation for cyclists 14. Aerobic Endurance analysis 15. Intervals Analysis 16. Training Planning 17. Integration with Oura 18. Aerobic efficiency and cardiac decoupling Other 1. HRV normal values 2. HRV normalization by HR 3. HRV 101 |
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