Category Archives: Heart Rate Variability

Feedback While Training – Stayfit & Breathe Sync

When I started looking at Heart Rate Variability (HRV) as a tool to train myself I was drawing on my experience using heart rate monitors for physical training. When I went for a run I would see my heart rate in real time and adjust my exertion accordingly. I found this a powerful way to both increase my fitness and extend my training by not overdoing it.

Most of the apps today either lack context on the data they gather or give you a passive report on a past period of time. For example, the Jawbone UP tells you your steps but it is up to you to index that against other measures to see if you are improving your fitness. Multiple HRV apps will give you a coherence or stress reading after a session is complete. Two apps I am using now structure the feedback in ways that make the experience more interactive and provide good enough context for a user to take action in real time.

Stayfit by Marco Altini. I have just started using this app and really like it. It does not use HRV, but it creates very nice context by indexing resting heart rate against daily exertion. A quick measure of resting heart rate in the morning is very easy to do, then watching your exertion the rest of the day helps you work on fitness. The interface is very clean:


I find that I look at it often during the day to watch my kilocalories expended and make adjustments to my schedule and activities to increase exertion for the day. It is only available on iOS is its only drawback.

Breathe Sync by Michael Townsend Williams. I have written about this app in an earlier post and still have it as one of my go to apps. The reason is that its primary use case is to bring you back to a coherent and relaxed state very simply and quickly. It does give a measurment but that is a secondary part of the experience. The camera on your phone picks up your heart beats and then shows with a simple blue and white ring visual how your heart rate is slowing or speeding up as you see here:


Over the course of the session the ring visual will allow you to match your breath with the increase and decrease of the interval between heart beats. Very powerful and effective. I use it when I feel amped up or just prior to a meeting to get into a balanced place.

The context of indexing one measure against another in Stayfit and the very active intervention quality in Breathe Sync put them both on my daily use list. Ultimately I want to train myself to use awareness and respiration to set myself “in the zone” when it comes time to negotiate, interview and brainstorm in a professional setting. These two apps are great tools as I work on getting there.

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Heart Rate Belts, Phone Cameras and Convenience

I had a chance to have a coffee with Marco Altini, the builder of the Heart Rate Variability Logger app that I often use to take readings. I enjoyed the discussion as Marco is very knowledgeable on the topic of heart rate variability. I took some key insights away that will help me set direction for future studies.

During the discussion he told me he is focussing on his app that support physical training, HRV4Training. He prefers to work on this because in addition to a bluetooth heart rate belt the user can choose to take a reading with the camera on the phone. Marco thinks that the convenience of using the camera makes it more accessible.

I agree with him. In my own work I often to not take advantage of readings because I don’t have the belt on and simply don’t feel like putting it on. Just this week I did one reading while conducting an interview using the belt, and I did not take readings on numerous meetings that would have given me good data for further study.

And while pushing into new areas of study such as heart rate variability during negotiations, or while giving a speech, it is not going to work to have a finger on a smart phone camera. To only use the camera would confine readings to stationary sessions where no activity was allowed. There is much more to learn than taking readings in only a motionless state.

So I am going to start incorporating smart phone camera useage into my work and share the results here. Marco has done a workup of how his apps use the camera to compare well with the Polar H7. We have to figure out a way to make this accessible, and useful, so more people can train for improved personal performance using heart rate variability.

Superpower Series: Variability Basic Training

Before you begin taking readings in work sessions and meetings you have to become familiar with the pattern and connection between your circumstances, Heart Rate Variability (HRV), and breath. Your breath rate signals to your nervous system whether your circumstance calls for an accelerated state, or a relaxed nervous state. Conducting repeated sessions will allow you to see the relationship.

Exercise: Using basic kit take a measurement each morning for five minutes. While doing so, breathe six times a minute. That means breath in five seconds and out for five seconds. You can start with a smaller period if you are uncomfortable  and need to practice. Even at smaller intervals make the breaths even and consistent. Afterward look at the intervals between heart beats to see how well your breath and HRV relate to each other.

If you are relaxed the measure of RR intervals will go up and down evenly with your breath. This means your Parasympathetic Nervous System (PNS) is applying the brake to put you in rest and digest state. Here is a graph of my RR intervals during a five minute session in a completely relaxed state:


I have had many sessions where despite regular breathing I could not enter a relaxed state. Here is a session where I was thoughtful about a variety of to do’s while trying to bring myself to a relaxed state. These Upsets were evident in the graph of my RR intervals:

You can see in the intervals have periods where there is not much variability. My thought process was accelerating my Sympathetic Nervous System even though I was sitting quietly breathing in a regular rhythm. In another session I was generally relaxed and in the zone then had a thought that interrupted my flow. I let the through go and returned to breathing and recaptured my variability. You can see the interruption and return in the red circle.


In another session on two occasions I had Upsets in the flow of the session and was able to recover twice. You can see these episodes in the red circles in this chart.


The exercise of breathing regularly and taking your HRV measurement for five minutes a day will give you a baseline for when your system is Upset by different thoughts, and when it is responding to your breath while relaxed.

If you want to learn more about developing a Superpower read about Giving a Speech.

Superpower Series: Why You Should Memorize Your Speeches

One superpower that some people seem to have mastered is the ability to stand in front of a group of people and give a speech. For most people it is the most stressful of events, up there with losing a job and divorce. So how can you use Heart Rate Variability (HRV) to keep your fight or flight mode from kicking in and you entering a panic state in front of the group?

Well, it does not appear you can avoid the fight or flight response standing in front of a group of people. From measurements I have taken when speaking I think that the only strategy you can employ is to have more material embedded in memory so you just speak automatically without having the engage your prefontal cortex.

The mechanics of this are straightforward. When you are in fight/flight your body optimizes blood flow to get you out of danger. Blood flows to your limbs and the back of your brain, allowing you to maximize your ability to react. When you are in this reaction mode your thinking brain is offline. You can’t wing it when your thinking brain is offline.

I took readings while speaking at two different Quantified Self meetups. This is a very sympathetic crowd. There is no pressure to perform for this crown. And I have experience speaking publicly, from corporate engagements to speaking competitions for Toastmasters. I enjoy public speaking, so I should be on the more relaxed end of the spectrum. The data shows that even experienced speakers are not immune to the stress of presenting to groups.

As a baseline for compare readings from a meeting with senior people that I am working for as I presented in an earlier post. This was a high intensity meeting where I was expected to present information. The graph shows with blue bars where I experienced the fight/flight impulse.

Readings on a speech I did at the meetup July 28th of 2014 showed how much stress the system kicks in when on a stage. I started the measurement about five minutes before the speech and did some breathing exercises to see if that would have an effect on my measurements. Here is me giving the speech.

Qs Speech

The breathing exercises did help kick in my relaxation response for the first five minutes of the reading. Once I got to the podium, however, the fight/flight kicked in. I spoke for 14 minutes and answered questions for ten minutes. You can see the readings in this graph: The red box shows the period in which the speaking portion of the presentation took place.


A second speech showed a similar pattern. In March of 2015 I spoke again at a Quantified Self meetup to a smaller group. Again a very sympathetic group. I knew the material and was pleased to be presenting. This was a shorter speech, five minutes speaking and five minutes of Q&A. You can see from the chart and the red box that the during speaking portion I was almost entirely in fight/flight state.


Why this is important is  as described above the pre-frontal cortex is offline when in this state. Meaning that you can’t think through what you are going to say in real time when you are on the podium. You are in reaction mode. So rehearse the material. When a slide comes up, you react to what you have memorized. I have had experience of “watching” myself giving a speech when I have memorized the material and am bouncing along well. And I have had the experience of freezing in place when I had nothing in my deep memory to react to. And I just stared blankly at the audience.

So memorize your material before you get up to speak. Your physiology will ensure your brain is offline. If you react well throughout the speech you will give a great speech. Even this guy had to memorize his speech:


HRV Tutorial – Measurement Times

One important dimension of your measuring that is important to understand is how the length of time that you measure. Heart Rate Variability (HRV) is the variability of your heartbeats over a period of time. The standard readings (rMSSD, pNN50, etc) are based on some reading over a specific period.

That means if you are studying the effect of eating donuts on your HRV you need to ensure that reading 1 and reading 2 have approximately the same length (5 secs, 30 secs, 2 mins, etc). I prefer 30 seconds snapshots. Readings of different lengths are apples and oranges because you are getting an average over that time period.

If you eat a donut and read your HRV for 5 minutes the reading will an average for the 5. Eat the second donut a day later and read for 35 minutes you will get the average for 35 minutes. If your blood sugar changes more during the 35 minutes simply because your body has more time to digest it will look like a lower number on day 2 and you may draw wrong conclusions based on an error of measurement.

If all other variables are kept constant and you vary the measurement times you will get incompatible readings. Make sure you keep an eye on your timer and know that the similar timing of your readings are your most important source of useable measurements.

HRV Tutorial – Setting Up What You Study

After you have your basic kit you can start taking readings and compare numbers. To save time and avoided taking readings that don’t compare well to other readings it is important to do a good job defining what you are looking to study. This helps keep what you are reading consistent and easier to implement.

Primarily you will be looking at the difference in your Heart Rate Variability (HRV) as you vary conditions in your environment. For example, if you decide to look at the effect of sleep on your HRV you will have to pick a time, conditions and length of time that you will measure your HRV.

For example, if you read your HRV each morning as part of your sleep study, you have to understand that reading HRV immediately after waking is different than 30 minutes after you wake up. Your SNS and PNS are in a different state during those two periods. Additionally, if you walk upstairs to retrieve you heart rate belt on one morning and you didn’t the day before, the two readings will not be comparable.

So it is best to define precisely what you are going to do when you take your readings. In your sleep study example write out “Two minutes after I wake up I take my reading with my heart rate belt reading to the app for 5 minutes as I lay on my bed.” Each morning that you meet those conditions include that reading in those you compare. If one condition is violated, unfortunately, you will have set those readings aside.

Find out more by reading about Measurement Times.

HRV Tutorial – Basic Equipment Setup

Because of the limitations of pulse oximetry I recommend you start with a Polar H7 heart rate belt. It is affordable (about $79) and available on Amazon or a local sporting goods store. If you don’t choose an H7, ensure your heart rate belt is Bluetooth Low Energy (BLE) so it syncs with the updated iPhone or Android device. Garmin uses a different standard (Ant+) and won’t work with what you want to do.

There are many, many apps that will take the readings from your Polar H7 and convert the data. The three best are iThlete, SweetwaterHRV and Marco Altini’s Heart Rate Variability Logger. iThlete is limited in that it is for a daily, short reading to determine your state of physical training. SweetwaterHRV is a good app made by very nice people and it is a bit difficult to extract data (you download and email it). It has a lot of interpretations of the data in the app.

Marco Altini’s app gives nice readings in real time and has a dead simple Dropbox or iCloud download feature. You take a reading, press a button on your device and the .csv file is in your file folder. That simple. Once you have a .csv file you can import it to excel and play with the numbers. You can also see the derivations and start looking there.

Find out more by reading about Setting Up What You Study.

HRV Tutorial – Sensors

You will have numerous sensor available to you and they break two types. One type uses pulse oximetry, which shoots light through your skin to sense the heartbeat by the change in color of your skin based on your blood flow. When you use a watch (Apple Watch, Mio, Basis, etc), an ear clip (Heartmath), or a finger clip (as in those common in hospitals), they all use pulse oximetry.

This type of sensor is good for measuring heart rate, but NOT as good for Heart Rate Variability (HRV). This is because the way it measures heart beats will have a lot of errors when you move your body. There are medical studies on these error rates. Nothing wrong with your Apple Watch telling you your heart rate on a run or during the day. But if you are trying to get precise HRV information from that same watch while you are moving around you will have a problem. So you can use pulse oximetry if you plan to be motionless for your studies, but if you want to look at anything where you move your body you will need to use a different method.

The way to accurately measure your individual heart beats and then your HRV is based on reading the electrical impulses that make your heart beat. These sensors are heart rate belts or more expensive adhesive patches. These give you the required accuracy because they are reading the electrical output from your heart when it beats. I have tested pulse oximetry (Heartmath, Mio wrist band) vs Polar heart rate belt and the differences in accuracy when in motion are noticeable.

Find out more by reading about the Basic Equipment Setup.

HRV Tutorial – How To Get Your Numbers

You capture the Heart Rate Variability (HRV) measurement as expressed in RR intervals by using a sensor and having it read its output to a software application with which you can see a display of the data or download it for viewing and manipulation.

To get your HRV readings from your body you can use a heart rate belt or other type of sensor and read the output on an app. To actually play with the data you will have to find an app that downloads the data in a format such as .csv or .txt that can be ported to a program like excel or R.

To learn how HRV works, I highly recommend you start by looking at the RR intervals so you can get familiar with the source data. Using apps that have already derived some measure is easier once you understand the underlying mechanics of the RR intervals. I wasted a lot of time trying to understand the apps before the underlying mechanics. You can avoid that.

Find out more by reading about Sensors.

HRV Tutorial – RR Intervals

Heart Rate Variability (HRV) is measured by looking at the time interval between successive heart beats over a specific period. That means that if you examine ten heart beats, there will be a difference in intervals between each successive beat and those differences are averaged into some number that indicates there was either a lot of variability between all of the beats or very little variability during the period the ten beats occurred.

The way HRV is captured is by a string of numbers called “RR Intervals.” The RR Intervals are measured in milliseconds. For perspective, a resting heart rate of 60 beats per minute means that there is an average of one heart beat per second. The difference between two of those beats will be a percentage of that once second, so milliseconds are the best unit of measure.

All of the complex measurements that you will encounter  (Fourier transformations, High Frequency/Low Frequency, rMSSD, pNN50, etc) are all derived from this string of numbers. It can be hugely frustrating looking at academic papers and articles/blog posts without understanding that because they all dive right into these derivations and at first it looks like HRV has scores of different measurements. It is one measure with a lot of interesting interpretations. And you will develop your own favorite over time.

Find out more by reading about How To Get Your Numbers.