This recent email exchange between a customer and ithlete founder Simon Wegerif discussed several interesting and useful points. So, with the customer’s permission we are sharing it as a blog post. Some of the questions covered include:

  1. The accuracy of ultra-short HRV measures – is 60s enough?
  2. What is the relevance of breathing to HRV?
  3. The importance of independent validation for HRV apps (and in fact any health app)
  4. Can you compare the numbers given by different products that measure HRV, and if not, why?
  5. Why has the LF/HF ratio fallen out of favour as an HRV measure?
  6. Why is recording context with your HRV is so important for interpretation?
  7. Are all HRV readings able to provide the same information?


Hey guys,

I use your normal app to track my daily data like stress and sleep and all that. I find the display of data VERY useful to get an overall feeling of how my data reflects on my HRV measurements.

I also use a second app to measure my HRV. So, this brings me to 2 main reasons why I haven’t made the move to a paid version of your app yet:

  1. Is I was never clearly offered the reason to pay for the Pro version in the app. So, to this day I’m still not sure what the benefits could be.
  2. But more importantly – because your app only takes a 55s reading (and forgive me if there’s a way to change that length – I haven’t found the place yet). But because of the short reading interval – the HRV readings are always inaccurate. I’ve compared them to two other leading HRV apps and yours is consistently off.

In fact, I’m not even aware that I got myself on to your Pro version trial in the first place. I may have clicked on the link in the app home screen, but no message came up to tell me any details…

I love using the free app for the dashboard though. I find it really intuitive and as I said – easy to look and get an instant clue about the patterns in the relationship between the data and my HRV (I use the HRV from my other app though).

Thanks for asking.


Hi Anita

Thanks for the feedback, that’s very helpful.

I would like to pick up the second point you make, because ithlete is in fact the only HRV app that has been independently validated (please see so I’d be curious to know how you came to the conclusion that it is not accurate?  Can you tell me what sensor and phone you are using and what you are comparing it to?

I’d be very grateful to clear this up!



Hi Simon,

Thank you for taking the time to enquire further.  

Firstly – I must emphasise – I’m relatively new to HRV and willing to learn.

So, my feedback is based on personal experience and what I have read in my research. 

The other app I use in conjunction with yours is the Sweet Beat Live – white labelled to Bulletproof Exec as Stress Detective. That measures HRR and HRV (in different sessions). Their measurement session is 3 minutes.

Independent reports say that 5 minutes is the sweet spot for HRV measurement duration. My main concern was that ithlete only takes a reading for 1 minute.

With all that said – I use the Polar H7 chest strap to measure and have the iPhone 6S.

Some days ithlete and StressDetective would be within 1-2 points of each other – which is fine. But other days there are as much as 20 difference. Days on which I feel not in top shape – which is reflected in the SD reading, but ithlete will give me a reading of 80+…

After reading the material you have on your site – I don’t know what to think :o)

If you had to state it in very simple terms – why is your 1min measure more accurate than the usual 3-5 minutes?

Secondly – I must also say that I love the dashboard your app provides. It’s (as you say on your site) one of the simplest ways to quickly see how all the other factors affect your HRV score :o)


Hi Anita

Thank you also for your openness – I will try to respond in a similarly open manner!

Modesty aside, I was the inventor of HRV on the smartphone – having read some fascinating research on HRV in 2008, I decided to quit the day job as an executive at Philips Electronics and create an app that was consumer friendly & convenient, but scientifically valid. My initial motivation was to help myself train for endurance sports more effectively, so I could keep up with more talented and sometimes younger training partners. We now have a fast-growing business, and ithlete is used in medical, pharmaceutical, armed forces & sport science research. We also white label apps for other people.

My background in consumer electronics made me acutely aware that if someone is going to do a test every day, it had better use the minimum amount of time. I did set a target of 60s, and didn’t know whether it was possible for the reasons that you mention. However, the use of paced breathing and just parasympathetic HRV (HF / RMSSD) meant that 7 breath cycles was sufficient. This was doubted by many researchers until it was independently validated by (Flatt, Esco 2014) taking 10s, 30s, 60s segments out of a 5-min measure & seeing how well the very short measures agreed with the 5 mins. As you can see from the 3 charts on the same scale, the agreement improves very significantly from 10 to 30 to 60s, and many other studies have also found this.

With respect to the HRV number that is reported, these are not directly comparable between apps. We have been awarded US and international patents for the 1 minute paced breathing measure, colour coding the results and the number scale. There are some apps such as Bioforce and Vitality Rx that have licensed this scale but others that haven’t, so they have used their own.

Finally, your comment about high HRV is also relevant – as with almost everything in life you can sometimes have too much of a good thing, and I wrote a blog post to explain this.

I hope this all makes sense, and is helpful to you. Let me know any other questions.

Kind regards,



I really enjoyed the article – very thorough. I don’t believe this is the case with me, although I know I have an underlying (or overlaying) chronic anxiety issue that’s showing up in my LF/HF ratios.

Strangely enough these come perfect when I’m exercising…  

I really appreciate the time you’re taking to explain ithlete to me – seems this is a pattern with you – you take a lot of care to interact with people on your site too.

As I mentioned – I’m very new to this. I am a quick learner and love learning – but it will take me some time to dig into enough info to make up my own mind. In the meantime – there’s a massive gap for easy to follow information on how consumers like me could use HRV via your app (or others) to actually optimise their stress levels and their training.

For example – the article you pointed me to about the overtraining effects on HRV readings. If I read it 3 times, I’d probably obtain some sort of a useful conclusion for myself as an end user that’s not a pro in the field.

And I am stubborn hen it comes to getting clear on something. But I still don’t get the working knowledge of what the article talks about, meaning I’m unlikely to use it. 

So – I’m not telling you all of this for egotistical reasons – just pointing out that I want to get more out of your app – but for the moment all I can confidently do is measure HRV, trust the traffic light indicators for training (without any skill to help me interpret any abnormalities or long-term patterns that are specific to me). And use the self-evaluation sliders, that I find very good idea, but again – in the long term no easy way to interpret the patterns I collect…

Also – as a serious exerciser (not athletic level) one of the ways to see improvements in my training is to measure HRR, and to look at my LF/HF ratios. With the current app version I can’t see those. Perhaps in the Pro version I can? But I don’t know.

Anyway, sorry for carrying on and on, I’m simply saying that I love the passion with which you talk about the topic of using HRV to optimise your own performance, so I guess what I’m trying to verbalise is that it would be great to see a simple to follow, all-in-one guide to using HRV to optimise stress and sports performance as a non-athletic pro.

If that’s not your focus as a business – then sorry for the rant :o) 

As an aside – do you have any plans to do a joint project with one of the leading companies in the emerging Nutrigenomics field? Like DNAFit for example. Seems to me that their information about how a person is “built” genetically to recover, injury likelihood, neurotransmitter inefficiencies and muscle finer types, combined with your knowledge of using HRV for athletic performance and training results, could be a powerful combination.

I’m not aware of anyone doing the two things together. At least not for end consumers. I’m assuming for professional athletes all sorts of amazing things get done behind the scenes :o)

Wow – this is a long email. 

Thank you for creating ithlete. I understand it much better now, and will make sure I share how great it is with my crowd.

Have an awesome day,



Thank you very much also for taking the trouble to reply so comprehensively. Such feedback is really useful to us as we (try to) make the transition between early adopters and the mass market that can benefit from daily HRV measurement.

I want to pick up on a couple of points you made:

  1. LF/HF ratios. Although these were considered useful in the early days of HRV (80s, 90s), it has since been shown conclusively that LF is not the indicator of sympathetic activity that some had hoped, and is in fact most likely an index of what’s called ‘baroreflex gain’ which is the ability to regulate blood pressure (particularly to the brain) when moving from lying or sitting to standing (without fainting!). We posted a guest blog on LF/HF to explain in more detail.  In the meantime, the author now has his PhD and is actively researching this area in the US.
  2. Improvements in fitness. Resting HR is by far the best metric to track for showing this, because it includes the effects of physical changes of the heart (pacemaker region) as well as autonomic (i.e. vagal nerve input). There is a simple way to estimate your VO2 max which is MaxHR/RestingHR x 15.2. So, the lower your resting HR, the higher your VO2 max!   HRR only measures parasympathetic reactivation, and to be honest, its interpretation is not well researched (more articles on our blog on this…)

You make a good point about coupling HRV with nutrition, subjective metrics and providing the user with meaningful actionable feedback. That’s our mission over the next year, and perhaps I can come back to you when we have things that we think are ready?

All the best again, hope this is helpful


Oh Simon – now you’ve crushed my little experimental world right down :o)

This is absolutely fascinating. I’m going to retract and do a lot of reading on the topic on my own. Please know that I am an even bigger fan of ithlete now. 

In July I start a Coaching certification with Dave Asprey and it will be interesting to get to understand more about why he chose to white label the Sweet Beat Live app…  

As it happens, in the biohacking mastermind I’m a part of, we happen to come across your name. My friend Ines O’Donovan mentioned that she met and spoke to you about ithlete in the last Biohacking European conference. We both agreed you know your stuff :o) 

I appreciate you taking the time to reply to my questions. I would love to be a guinea pig for any version of ithlete you decide to put out for normal peeps like me, so let me know if I can be of help in any way. 

Have a good week end.


Hi Anita

That’s cool – what a small World!  Indeed, I enjoyed chatting to Ines at the Biohacker summit in London.

I think we were introduced by Damien Blenkinsop of podcasts. I did an interview with him shortly after he started the series.

I will certainly bear you in mind for future revisions, and thanks for offering :-)


Hi Simon, Happy New Year – I hope you’re well.

A few months ago, we exchanged a few emails about best ways to measure HRV. Nowadays with the advent of the Oura ring and with Apple Watch measuring those how are you finding that is affecting ithlete? 

I ask because measuring with a chest HR monitor, the Oura and the watch gives severely different numbers. I suspect that it has to do with the tech, but also with the frequency of measurements and the circumstances of measurement.

I hope you don’t mind me emailing you out the blue with this, but I just can’t find reliable – well explained information on this – and you’re the one person who has displayed solid knowledge on the topic since it’s infancy.

Why would you say this discrepancy is so big? Is there a single guide/source of info I can immerse myself into on this topic that would help me use the HRV data in a way that will enhance my overall wellbeing?

Are you aware of how Apple is planning to enter the HRV interpretation market? 

Thank you – I always appreciate your opinion.


Hi Anita,

Happy New Year to you too!

I remember our exchanges of a few months ago. Awareness of HRV is growing quite fast now, and is so much higher than when we started in 2009 (nearly 10 years ago already!). At the start, the ithlete product was revolutionary because HRV could not previously be measured in an easy to use low cost way. It was adopted by researchers (who later validated its accuracy) and health practitioners around the World. Our target audience for ithlete though was always the motivated athlete looking for tools to help them optimise their training.

Of course, HRV can also be a great barometer of overall health, and it is this aspect which is being picked up by newer entrants such as Apple and Oura. The Apple Watch HRV measurement is actually SDNN, a different and more general measure to the RMSSD used by ithlete. SDNN reflects all sources of variation in heart rate, whereas RMSSD focusses on parasympathetic activity related to breathing. That’s one reason why the numbers are not comparable. The circumstances are also different – the Oura ring measures HRV in 5-minute segments during the night. They do explain on their website that the numbers obtained will not be the same as the dedicated HRV recovery measure which ithlete gives after waking. Being the first, we patented this aspect and although we have licensed it to a number of companies, Oura is not one of them. We also recommend performing measures in an upright position as this shows greater sensitivity to recovery in athletes due to an effect called parasympathetic saturation.

In summary, different HRV products will give different numbers due to the measure (and scale) they use, body position, time of day and the type and quality of sensor used. The growth in the market has brought specialisation. We at ithlete provide the most comprehensive and accurate tools for assessment of recovery, whilst other manufacturers either have different applications in mind, or are aiming to provide an entry level introduction to HRV. Most products will chart daily rises & falls in HRV and trends, but leave it to the user to figure out why those changes are taking place. Conversely, we want to tell the athlete or active individual not only what is causing the changes but how they can use that information to optimise their training & recovery. We are about to introduce elements of AI and machine learning to our products to assist with this, and I hope that with 10 years of dedicated work we can still stay ahead for a while longer!

If I was to recommend just one article that everyone should read about HRV and how you can use it to get healthier, I would say read Todd Becker’s blog Track Your HRV to Boost Adaptive Reserves.