Podcast, Recovery, Science, Technology, Training

Heart Rate Variability (HRV) – Applications and Insights in 2018 and Beyond with Marco Altini | EP#144

 August 27, 2018

By  Mikael Eriksson

​​​​​​Heart Rate Variability (HRV) - Applications and Insights in 2018 and Beyond with Marco Altini | EP#144

How should triathletes, runners, cyclists and other athletes use and apply heart rate variability (HRV) in practice, to actually improve their response to training? And what other insights are there to be gained from measuring HRV? Data scientist Marco Altini, founder of HRV4Training, has the answers. 

Discuss this episode!

  • Let's discuss this episode and the topic in general. Post any comments or questions in the comments at the bottom of the shownotes. Join the discussion here!

In this Episode you'll learn about:

  • The main practical applications of HRV and how to use it to guide training and recovery needs.
  • Short-term (daily) vs. long-term (7-day rolling average) HRV pros and cons. 
  • Potential drawbacks of HRV: can it cause athletes to hold back unnecessarily?
  • Additional insights made possible with daily HRV measurements and the HRV4Training app.
  • The latest trends in the HRV field of research. 
  • The future of HRV research and HRV4Training.

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About Marco Altini

5:15 -

  • Marco is the founder of HRV4Training.
  • His background is data science and he has a PhD in Applied Machine Learning from Eindhoven University.
  • He has published 40+ papers and has a number of patents in the field of health technology and sports.
  • He is also involved in another digital health startup called Bloomlife which focuses on helping expectant mothers have a healthy pregnancy.
  • Marco is also a passionate runner. 

Practical applications of HRV4Training

6:17 -

  • As HRV reflects physiological stress in the body it can be used in different ways.
    • Stress is the result of any factor within our lives.
  • The ability to assess stress objectively can help us make small or large adjustments in the pursuit of performance.
    • It can help us find a more balanced profile.
  • HRV is used so much in the context of training because the stress of training can be easily quantified.
    • It's one of the larger stressors we face, particularly for athletes.
  • It's easier to see the feedback loop between training and recovery:
    • Using HRV to quantify recovery and then using that information to plan training.

Adjusting training based on HRV

8:43 -

  • The first thing is to have a good training plan - HRV cannot be a replacement for this.
  • There can be a misconception when you get started and you measure your HRV and things look good, then people tend to see that as license to go hard every time.
  • It's best to have a good training plan, possibly a polarised training plan, and then use HRV to make it more individualised to yourself.
    • We all respond differently. 
    • Even if you work with a good coach and your plan is personalised to you and your lifestyle, HRV can add objective feedback of how you're responding.
  • This information can be used to look at data variations and acute changes.
  • There is research suggesting that high intensity workouts should be planned when HRV is trending well.
    • Or, it shouldn't be planned when HRV is particularly low.
    • It may be good to reschedule this workout to a time you may be better suited for it.
  • Looking at day to day variability can be an easy way to start looking at HRV.
  • In general if you're adapting to a specific training block, you can use it to identify positive adaptions.
    • This would be a change from the baseline (7-day rolling average).
    • If you're not seeing these changes, you can make adaptations to the training plan.
  • For elite athletes, training 1-2 hours a day is the bare minimum and their HRV is generally higher than the rest of the population.
    • There is more room for variability.
    • In these athletes, typically the baseline changes can be really useful information.
  • For recreational athletes who train less or less frequently, the training stimulus will already be a significant stressor.
    • This may likely be bigger than their normal baseline stress, so they can use their daily HRV changes for feedback each day.
  • Big sessions often have a big impact on the following day's HRV.
  • You can always look at big sessions because they have the least 'noise', but you can look at day to day variability on a more micro level.
  • Baseline here is the 7-day rolling average of HRV.
    • This is usually quite representative of underlying physiological stress.
    • This is all available in HRV4Training.

Baseline HRV

14:46 - 

  • When we look at physiology, we need to take a bit of a different approach than the usual 'higher (HRV) is better'.
  • With HRV and physiology, the way we should think is 'normal is good'.
    • When things are at 'your normal' it means everything is going well.
    • Abnormal physiological variables is what you should be worried about.
  • Reductions in baselines may suggest some change in the plans - you may need to slow down a bit.
  • If you don't see increases in the baseline but everything is within your normal values, this would suggest things are going well.
  • It's important to collect your own data for a while and don't implement changes straight away.
    • You need to see your own physiological response to a couple of your training cycles and/or a couple of hard sessions.
    • Depending on the person, day to day changes for or baseline changes may be more useful. 

Recovery Points

17:37 - 

  • rMSSD is usually used to measure HRV in research, but in HRV4Training this has been simplified to 'Recovery Points'.
  • rMSSD reflects the beat to beat variability, which is typically something between a few milliseconds and 200 milliseconds in the general population.
  • Regular individuals probably are on average in the 20-30 milliseconds range, but elite athletes tend to have higher values.
  • Recovery Points are derived entirely from rMSSD, but they use a different scale.
    • We take the logarithm of the number, and multiply it by 2.
    • This is because humans tend to like numbers in the range of 1-10 - even though Recovery Points can sometimes go beyond 10, but it's usually in the 5-11 range.
  • When you measure the first few times you will have a value that's your baseline and you won't deviate much from that.
    • Much of your normal HRV values comes down to genetics.
  • While with some lifestyle changes (e.g. going from unhealthy to exercising well, improved sleeping habits, etc.) can certainly make changes in your baseline, normally much of it is genetics.
  • Therefore the changes you see on a day to day basis will reflect stress and recovery.
  • In the context of heart rate, it's clear that a lower heart rate reflects higher fitness level.
    • Especially if you take someone who isn't training much and they go through an exercise program, you will see a reduction in resting heart rate.
    • However you will not necessarily see an increase in HRV.
  • HRV is better used as a continuous feedback loop that helps you assess recovery and make adjustments, more than an overall marker of fitness.
  • There is a relation with fitness, but it is very weak.
  • Although some elite athletes do have higher HRV, it isn't a strong enough link.
    • It's different from measures such as VO2max where sedentary individuals will have a low value and elite athletes will have a high value.
    • If you take HRV, you could easily get some people mixed up.

Does following HRV hold athletes back unnecessarily?

23:09  - 

  • A recent study published put runners through a training program before a 10K, and they had one group skipping the hard sessions when their HRV was below their normal values or trending negatively.
    • They found that the group that used HRV to guide their training performed better than the groups doing all the workouts according to plan regardless of HRV, who often did more high intensity sessions.
    • This shows that in general, holding yourself back when you are not physiologically ready to take that kind of load, can make you perform better in the long term.
  • In general, it's partly the case that people tend to go too hard too often.
    • Even doing the switch to polarised training can be hard for some athletes - spending that much time as low intensities.
  • HRV can be a way of getting more aware about your body's response in general, and the intensities you should be keeping.
  • Holding back too often is not really the main problem.
    • Particularly as HRV values being lower than your normal, statistically speaking, is not something that can happen too often.
    • You take a margin which is unlikely to be where your daily score is.
  • There is always a trade off between how big the window of normal values is​:
    • If you take a long window you might be able to understand better when baseline values are outside your normal, due to major stressors.
    • If you take it that long you might also miss physiological adaptations and miss what you called your normal a long time ago.
  • We decided that using the past 60 days was a good way to manage this.
    • In the app we use this window to understand your normal physiological ability.
    • Then in that way on a day to day basis we look at where your score is in respect to the past 2 months.
    • This is used to determine if stress is significantly higher and provide advice that way.
    • This is a good trade-off because you can keep account of acute changes in the short term but also things happening over a couple of weeks.
      • This can be the case if there are other major stressors that are not just intense workouts (e.g. work, family, travelling).
  • In general, my understanding is that if your HRV is too low, you don't have to totally skip the session but you need to reduce the intensity.
    • Depending on the athlete history you can have an easier session, not necessarily rest.

Additional insights from HRV4Training 

28:29 - 

  • The 'HRV trends' is one of the more interesting insights because we take an approach where we do not only look at your HRV score, but also at how your HRV has been changing in the past two weeks.
    • Again this is done with respect to your past two months scores as well.
    • We look at HR, HRV, the coefficient of variation of HRV (how much day to day jumping you have).
    • What has been shown typically is that you have a bit less jumping around (lower CV) when you respond to a certain training block.
    • We use the context of how well you responded to previous training to assess how well you're responding to the current training block.
    • It's an interesting insight because it doesn't rely on a single parameter.
  • There are other insights which are probably more specific to runners or cyclists. We can estimate VO2max or lactate threshold, without requiring specific tests, just from workout data.
  • As part of my research for my PhD and later with HRV4Training, we used data to try and determine what parameters were more representative of these predictors of performance.
    • This way people can track how things are going as they train and use it as feedback.
  • Other insights from the app are based around polarised training and training intensity distribution include training load.
    • There are standard chronic and acute training loads.
    • With the web platform that we just launched we tried to do some work on top of the typical output. You have to understand what your freshness or injury risk is in a certain week.
    • We are trying to get these things a bit more actionable like we do in other places in the app.
  • With the HRV trends, the user doesn't have to make interpretations themselves from specific numbers.
    • HRV4Training gives some advice by detecting the trend and telling the user if they're trending positively or negatively.

Using HRV in the athlete-coach workflow

32:54 - 

  • The way I would start with this is just to start measuring and collecting data.
    • You want to understand how an athlete responds to specific sessions, and also longer term training cycles.
  • Then, based on the individual plan you've built with your coach and the response of the athlete to certain sessions, start seeing if you can make certain changes.
    • Start to see if these variations in physiology make sense for what you see in adaptations and performance.
  • If you see things aren't trending well when the athlete failed to reach the state they were intending to reach, this can be a way to start using this information.
  • It can be included in the training plan, to eventually truly individualise the training plan to the individuals response to the stimulus.
  • Having this objective feedback of physiological recovery and stress can help you keep the feedback loop between training and adaptation closed.
  • The user can synch HRV4Training with Training Peaks so the values can become visible to the coach.
  • There is also a Pro version of the app for coaches.
    • It's a web platform and you can have you athletes all there and see their values.
    • We've built in several things that try to make the day to day variability easier to understand in the big picture.
  • It's clear in the web platform when all scores are going well - it's easier to make adjustments and act on this data from there.

Future of HRV research

36:08 - 

  • Now HRV is easier to measure thanks to the technology that has been developed in the past three years so there's a lot of research going on.
    • Both in elite athletes and in recreational athletes.
  • There's research focusing on taking things from the labs to real life, and on larger populations to see how parameters interact with each other.
    • It also helps figuring out how to optimise things in the long term.
  • Something I like is the research Sean Williams is doing.
    • He looks at training load and HRV a bit differently from others.
    • All the models from others relate to freshness and injury risk, which are typically based on training inputs (e.g. TSS from Training Peaks).
      • That information does not necessarily link to how your body has responded to the sessions.
      • These models don't take into account the physiology of the athlete.
    • Sean is looking at training load and HRV at the same time, both in the standard models but also looking at how these parameters change in respect to injury risk.
      • One of the insights that he had in his last paper was that a negative trend in HRV or a high acute chronic training load (which is a red flag for injury risk) taken alone were not predictive of injury.
      • When you paired them together, you had a much higher likelihood that the athlete would eventually get injured.
      • Combining training load and your own physiological response to that was more predictive of injury than any other parameters.
      • This is something that could possibly be extrapolated to other sports or different conditions - it was a small study in Crossfit athletes so it's different to endurance sports.
      • The findings make a lot of sense though, so looking forward to seeing more of this kind of work.
  • Mikael's note: I have my criticisms of Training Stress Score and encourage athletes not to take it as gospel.
    • If you look at an example: 30s run intervals x 10 with long recovery. The TSS is very low for something like that, just because the duration at intensity is very low.
    • The reaction of your body can be very different, especially for athletes who are more aerobic and slow twitch dominant. It can be a significant impact.
    • Together with HRV and the TSS maybe you'd be able to see this more.

The future for HRV and HRV4Training

40:46 - 

  • In the past 5 years there has been a huge amount of work making these things more user friendly and practical.
  • It's now easy to use and there are many more people doing it, which brings more awareness.
    There are courses that Jason More and I have put together, such as the HRV Course, which I would recommend checking out.
  • There is more information and awareness that it makes sense to measure your physiology and how your body is responding to the stressors.
  • What's next is to make it easier to interpret this data as it can still be a bit overwhelming and confusing.
  • In HRV4Training the next steps are towards planning a bit more.
    • Helping advanced athletes and coaches and providing an infrastructure where they can build things like training plans, follow their athletes and easily adjust things based on actual physiological responses.

Resources to learn more

42:53 - 

  • Go for an article on the physiological underpinning of HRV - e.g. Heart Rate Variability: a (deep) primer
    • You don’t need to get a PhD on the topic but it's important to understand that there's no magic.
    • It's measuring parasympathetic activity - the processes, physiologically speaking, are very clear.
    • You can get a little more confidence about what you're doing and what you're measuring if you understand a little more about what is actually being measured, and how that relates to training or other forms of stress.
  • Another one which is key, we talked a lot here about measuring HRV and the best practice - e.g. Summary of HRV measurement best practises
    • Physiology changes through the day to all sorts of stressors - e.g. having a cup of coffee, reading something upsetting online etc.
    • It really makes no sense to measure your HRV throughout the day, because you will just have a reflection of those stressors.
    • What you want to measure is your underlying chronic stress, which is why the app should be used first thing in the morning.
    • There are other things such as trying to stay consistent in body position and morning routine when you measure morning HRV.
    • These are also important to highlight for someone who is starting with this - to ensure they collect data that makes sense and will lead to useful insights.
  • Maybe also read an article on what to do once you've collected some of the data - e.g. How to use HRV to guide training: the basics.
    • Linking back to using it to adjust your training plan, not as a replacement of it.
    • Starting with small changes and looking at day to day variability as well as baseline changes and adaptations to specific training blocks.

Rapid fire questions

43:02 - 

  • What is your favourite book, blog or resource related to triathlon?
  • What is your favourite piece of gear or equipment?
    • Planning, being well-organised, consistency, not procrastinating. 
  • What do you wish you had known or done differently at some point in your journey?
    • Related to sports, maybe listen to my body more at the beginning. Polarised training and HRV came to me a bit late and brought significant improvements so it would have been valuable to start much earlier. 

Key takeaways

  • Have a good training plan - if everything goes well HRV wise, then just keep following that training plan.
    • If your HRV is in the red zone, that's when you should replace a hard session with an easy one instead to not stress the system too much.
  • This all relies on you gathering data consistently, in a consistent manner.
    • This includes measuring at the same time in the same position.
    • It helps you get a clear baseline, and to get a feel for how hard training sessions, lack of sleep or a night out might have on your HRV.
    • The more you collect this data and learn what your normal is, the more you'll benefit from using HRV.
  • Using an app like HRV4Training makes it so much easier to make interpretations of this data.
    • As you heard, the app is based on solid evidence and expertise, and is really good at making recommendations and giving advice and interpretations.

Links, resources and contact

Links and resources mentioned

    Connect with Marco Altini

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