May 29, 2017
In an article I wrote four years ago from one of the world's first biohacking conferences, hosted by Bulletproof Executive Dave Asprey in San Francisco, I jokingly quipped that…
“…here at the conference, I’ve seen a little bit of everything, but ultimately, we still need one device to rule them all – a la Tolkien’s magical ring.
In other words, we need one simple wearable unit to be designed that 24-7 tracks heart rate variability, heart rate, pulse oximetry, global positioning, sleep, steps taken, calories burned, respiration, perspiration and skin temperature.”
So I was understandably a bit excited when I discovered that exact magical ring two years later at another biohacking conference in Helsinki, Finland . It was called the ŌURA ring , and I immediately bought one upon discovering that it used state-of-the-art miniaturized electronics to track and measure a host of parameters, including sleep, heart rate, heart rate variability (HRV), activity, body temperature, movement, respiration, and more…
…all while being in airplane mode without constantly “irradiating” your body with an emitted cell-damaging bluetooth signal every 1 to 3 seconds like a FitBit, a Jawbone, an Apple watch, or any of the other popular self-quantification devices out there…
…and all while providing far more accurate data from a finger measurement rather than a wrist measurement.
After purchasing the ŌURA and using it for several weeks, I gave the full, nitty-gritty details on my experience in the podcast “Could This New Ring Be The Final Frontier In Self Quantification, Biohacking, Sleep Tracking, HRV, Respiration & More?“. Since publishing that podcast episode, I haven't taken the ring off since, even while deadlifting, swimming, cranking out pull-ups, sleeping, freediving, spearfishing and beyond.
Later that year, after spending oodles and oodles of hours testing my ŌURA, putting it through ringer (heh) and pouring over the data, I generated a big list of my own questions and also received plenty of questions from listeners and readers like you about how to interpret and make sense of data generated by self-quantification devices like this. In the follow-up article “11 Crucial Health Questions & Mighty Self-Quantification Ring To Rule Them All: The Official Oura Ring Q&A“, I answered 11 of the most crucial questions I received about the ring.
Then, after accumulating oodles of sleep data, including total sleep time, sleep efficiency, sleep latency, sleep disturbances, sleep heart rate and amount of time spent in each stage of sleep, including light sleep, deep sleep and REM sleep, I reported on how to use the ring for enhancing and quantifying sleep in my article “Everything You Need To Know About Sleep Cycles (And Four Ways To Hack Your Sleep Cycles)“.
So why this latest article on the ŌURA that you're about to read?
Frankly, for the past year, I've been speaking at and attending some of the top health conferences in the world, such as PaleoFX, the Ancestral Health Symposium, the Consumer Health Summit, the Biohacker Summit Series in London, Finland and beyond …
…and I've noticed that dozens and dozens of the world's leading physicians, health practitioners, biohackers, authors, professional athletes and beyond are all wearing this ring. And although it's readily apparent this ring has really caught on, I have found myself fielding dozens of questions from these experts about the latest developments in the ŌURA, especially with regards to the app interface, the sleep tracking capabilities, the temperature tracking capabilities, the new 24-7 HRV monitoring and more.
Last week, I reached out the good folks at ŌURA, and discovered that quite a bit has been going on at ŌURA’s secret lair in northern Finland over the past few months, including exciting news on the sleep validation front, as well as two new features. So, without further ado, let’s jump into these latest developments, shall we?
Enhanced Sleep Tracking Technology
This year, ŌURA went through validation sleep studies using their employees, as well one more formal validation undertaken with the Finnish Institute of Occupational Health. Up until now, no other wearable manufacturer, including ŌURA, had passed the muster of a peer-review study.
The prestigious Stanford Research Institute (SRI) opted to purchase two ŌURA rings during the ŌURA’s Kickstarter campaign, both a women's-ish size 7 and men's-ish size 11. SRI then compared the accuracy of the ring to standard Polysomnography (PSG) – the gold standard of sleep measurement – using forty-one healthy young adults. SRI found that the ring was able to accurately determine sleep duration 96% of the time and REM sleep 61% of the time.
It should be noted that the very best sleep study professional laboratories in the world are only in agreement 80-85% of the time and that some of the inaccuracies in detecting REM sleep were likely due to rings not fitting appropriately, given only two sizes were used during the study (ŌURA actually has a total of 8 different ring sizes). Additionally, ŌURA has improved their sleep algorithms a fair bit since the SRI study was completed.
A comparison of the histograms (sleep charts) for one of the SRI study participants is shown below:
Overall, these results are very impressive for a wearable ring, and far more accurate than other wearables currently on the market. You can read the full peer-reviewed study at “Massimiliano de Zambotti, Leonardo Rosas, Ian M. Colrain & Fiona C. Baker (2017): The Sleep of the Ring: Comparison of the ŌURA Sleep Tracker Against Polysomnography, Behavioral Sleep Medicine”
24-7 Body Temperature Readings
In addition to the Readiness Score, resting heart rate, and nocturnal heart rate variability (HRV) data that the ŌURA has already been producing for the past couple years, ŌURA recently introduced a view of nightly temperature trends to their ever-evolving app. Monitoring temperature trends can provide an insight into impending illness and can also offer women who are tracking their menstrual cycles valuable insight into the status of their fertility and health.
For both men and women, monitoring temperature can help with training guidance for improved fitness and general health follow-up via automatic detection of nocturnal body temperature (e.g. if body temperature is low during the night, recovery is enhanced, and if body temperature is high during the night, it can often cause poor sleep or indicate underrecovery). The ŌURA ring uses the minute-by-minute changes in skin temperature every night to determine your average core temperature. The trending of this data over several nights provides valuable insight into the your health by comparing daily temperature fluctuations to your established baseline instance. Consistent elevated temperature readings are often an early warning of impending sickness or overtraining.
The very cool (pun intended) thing that temperature readings may also be used for is to keep track of the phase of a woman's menstrual cycle. A women’s phase within their menstrual cycle provides guidance for their training volume and intensity. More specifically, the recent scientific study “Training and hormones in physically active women: with and without oral contraceptive use” suggests that women should restrict the amount of high intensity training during the latter half of their menstrual cycle.
More positive training adaptations can be enhanced by concentrating a higher proportion of intense training within the first half of the menstrual cycle. Admittedly, the study above focused on strength training, and while it is not 100% clear if these findings transfer to aerobic training, it is possible that the same principle applies to all training in general.
For example, Figure 1 below displays the temperature trend from the ŌURA app from a woman who is using hormonal contraception. She reported having a flu in early February – the point at which you can see elevated temperature readings.
As I alluded to earlier, temperature readings like this provided by the ŌURA ring, when used in conjunction with other sources of menstrual tracking, could help women keep track on the timing of their menses, and detecting different phases of their cycle. The temperature graph could also help determine the timing of ovulation and a women’s fertility window.
The general challenge with exact timing of the ovulation using temperature readings is that the elevated temperature is associated with progesterone hormone, which increases after the ovulation. Temperature graphs from three subjects are displayed below. For each subject, the upper picture has been plotted from the ŌURA website (nightly maximum temperature readings), and the lower picture displays the trend view in the ŌURA phone app.
Figure 2. Nightly maximum temperature readings (above) and the associated trend view in the ŌURA App (below) from subject 2. The ovulation day of the latest cycle was determined with urine test strips (yellow bar in April 14th).
Figure 4. Nightly maximum temperature readings (above) and the associated trend view in the ŌURA App (below) from subject 4. The ovulation day was determined with urine test strips during the last cycle.
In a nutshell, the ŌURA ring app update can now walk a woman through this entire process, and give her an instant readiness score based on her time of the month. In addition, both men and women can use these new constant 24-7 temperature readings from the ŌURA to learn a host of information about how their body responds to sleep, diet, exercise and more.
Heart Rate Variability Measuring All-Through-The-Night
The next feature ŌURA has recently added is constant Heart Rate Variability (HRV) measurements during your entire night of sleep. If you don't know what HRV is, then here's a handy list of resources I've produced about HRV in the past:
- Could This New Ring Be The Final Frontier In Self Quantification, Biohacking, Sleep Tracking, HRV, Respiration & More?
- A Deep Dive Into HRV: The Myths & Truths of Heart Rate Variability Testing
- HRV: The Single, Next Big Trend In Biohacking And Self-Quantification And How To Use It
- The Do-It-Yourself Guide To Using Heart Rate Variability Testing to Track Your Stress and Nervous System Health
- Everything You Need To Know About Heart Rate Variability Testing
Although HRV has always been one of many contributors which make up the Readiness Score that the ring gives you each morning to allow you to determine how ready your body is for training, stress, etc., the folks at ŌURA recently decided to show you all these nightly HRV readings in the smartphone app (mostly due to customer demand from nerds like yours truly who want to see what our nervous system is doing all the time).
So that means that the HRV number shown in the app when you wake up is now giving you the average of all the five-minute samples taken while you are asleep. For example, there would be 96 distinct HRV measurements for eight hours of sleep.
To make HRV readings comparable to each other, it is particularly important to standardize any HRV measurement with regards to the time of the day, prior activities and external stressors – including things like ambient temperature, noise and presence of other people. So nocturnal measurement all night long by a self-quantification device like a ring actually provides an excellent measurement tool for HRV – especially when you consider that all the other methods you'd have to use for this require the use of uncomfortable chest straps, which are not suitable for continuous use, constantly emit a radiating bluetooth signal, and can make it tough to sleep.
I'm often asked how exactly a freakin' ring on your finger can accurately test HRV when most other systems use bulky straps or wristbands.
That's a great question. Bear with me here, because this gets a bit complex.
If you were to visit a hospital or physiology laboratory, the gold standard method used to determine HRV would be an electrocardiogram (ECG), which requires a good skin contact via adhesive pads attached on skin (electrodes). The QRS complex of the ECG then represents the electrical activation that initiates the contraction of the heart. The time between the initiations of succeeding heart beats is called the R-R interval (see the figure below). Each contraction of the heart results in a blood volume pulse, which then propagates in blood circulation.
Schematic illustration of ECG and PPG signals over three heart cycles. One RR-interval and the corresponding IBI (inter-beat-interval) are marked with horizontal bars.
In contrast, photoplethysmographic (PPG) signals arise from blood volume pulse in the periphery, and this is the method used by the ŌURA ring. The ring sits on your finger and determines something called interbeat-intervals (IBI) – the amount of time between each beat of your heart – from PPG using invisible infrared light at a sample rate of 250 Hz (250 samples per second).
Studies comparing HRV parameters obtained by PPG and ECG have generally reported pretty good agreement, particularly when looking at measurements taken at night – but they have shown higher variability in PPG derived beat intervals, particularly in high frequency parameters . PPG has smoother signal characteristics than ECG, although the signal waveform also varies depending on heart contraction force and arterial stiffness. All these factors can increase the variability in the IBI data.
A variety of different HRV parameters are typically used in research and practical applications. If you want to take a deep dive, the methodologies of HRV measurements is presented in the Task Force committee report here. The most commonly used parameter is rMSSD, a time domain parameter which is an estimate of short-term components of HRV, and mostly reflects the “rest-and-digest” parasympathetic autonomic nervous system activity. In research use, five minutes has become a standard duration for short-term measurements, since shorter duration tend to give unstable results.
We already know that ŌURA ring provides you with a very comfortable experience and scientifically validated sleep quality metrics. It also handles several important factors that explain your Readiness to perform in daily life, many of which are partially determined by nocturnal HR and HRV. The sleep metrics of the ŌURA ring were successfully validated by Stanford Research Institute Center for Health and Sciences, yet the accuracy of nocturnal HR and HRV have not yet been published. Due to high wearing comfort, the ring could theoretically be a promising tool for long-term follow-up of recovery metrics.
So why not study all this and figure out if the ring really can be used for accurate HRV measurements? And that's exactly what ŌURA just gone done doing.
The purpose of the study you're about to read was to quantify the accuracy of the HR and beat-to-beat HRV measurement of the ŌURA ring. Since, as you've already learned, ECG based HRV is the gold standard method of measurement for HRV, the values provided by the ŌURA ring were compared to the R-R intervals obtained from the ECG in healthy individuals at night. The HRV numbers provided by the ŌURA ring were then compensated for the additional variance found in PPG based IBI data.
In the study, they measured nocturnal IBI data with the ŌURA ring (Oura Health Ltd, Oulu, Finland) and simultaneous R-R interval data with Faros 360 ECG device (Mega Electronics, Kuopio, Finland) in 10 healthy individuals (3 female, 7 male). All subjects had the ŌURA ring on both hands, resulting in 20 nightly recordings for analysis.
The ŌURA ring labels each IBI as normal or abnormal. Each IBI was included for the calculation only if 8 consecutive IBI values had been labeled as normal. They determined heart rate HR and HRV for each 5 minute sequence of the night (HR5min_ŌURA and rMSSD5min_ŌURA) as well as nightly averages (HRavg_ŌURA and rMSSDavg_ŌURA). Each 5-min sample was calculated only if more than 50% and 30% of the intervals were accepted by this criteria for HR and rMSSD. In order to compensate for the extra variance in IBI data compared to ECG, the ŌURA ring reduces the additional variation by rMSSDŌURA= √(rMSSDIBI2-202).
Kubios HRV software was then used to calculate ECG based reference values for the entire night (HRavg_ECG and rMSSDavg_ECG). In Kubios software, an automatic filter with medium setting was used to detect and exclude potentially abnormal R-R intervals from analysis. For the 5-min data, the same Matlab script was used to obtain reference numbers for both PPG and ECG (HR5min_ECG and rMSSD5min_ECG). In 5 min data the synchrony of IBI data and RR data was ensured within 5 seconds. The agreement between the methods was then assessed by correlation analysis.
So what were the results?
The comparison (scatter plot) between HR avg_ŌURA and HR avg_ECG is presented in Figure 2, and the comparison (scatter plot) between rMSSDavg_ŌURA and rMSSDavg_ECG in Figure 3.
Figure 2. Scatter plot on HR derived from ECG by Kubios software (HRECG) and the corresponding value from the ŌURA ring (HROURA) in the sample of 10 subjects, all wearing the ŌURA ring on both hands. Coefficient of correlation was 0.999 with a bias of -0.53 bpm by the ŌURA ring.
Figure 3. Scatter plot on HRV derived from ECG by Kubios software (rMSSDECG) and the corresponding value from the ŌURA ring (rMSSDOURA) MSSDadd) in the development sample of 10 subjects, all wearing an ŌURA ring in both hands. Mean absolute deviation was 2.1 ms.
95±7% of the 5-min sequences of the entire night had enough qualitative IBI data to be included for HR analysis. Within-subject correlation between HR5min_OURA and HR5min_ECG was 0.96 ± 0.02 (mean ± sd). 90±13% of the 5-min sequences of the entire night had enough qualitative IBI data to be included for HRV analysis. Within-subject correlation between rMSSD5min_OURA and rMSSD5min_ECG was 0.84 ± 0.15 (mean ± sd).
OK, I know that was dense. You still with me? Perfect…because here's the takeaway…
…in this study, near close to perfect agreement (r = 0.999) was found between the nocturnal HR determined by the ŌURA ring and that determined from ECG by Kubios Software. Also, strong agreement (r = 0.984) was found in rMSSD.
The reliability of the HR measurement was further confirmed in the short term (5 min) data. Among the 20 recordings (in all 10 subjects, both hands from each), the correlation between the methods was very high (r = 0.96 ± 0.02). For rMSSD, the corresponding results also showed high consistency between the methods (r = 0.84 ± 0.15).
So, in a nutshell, not only does the ŌURA measure your sleep cycles, HRV and body temperature all night long, but these most recent studies and updates have shown that it does so in about the most accurate way possible.
Don't get me wrong: from the NatureBeat HRV measurement to the WHOOP wristband to a newer wrist device I've been toying with called the LifeTrak Zoom HRV to a host of other measuring tools I'm constantly tweaking and testing…
…I'm not necessarily “married” to any one self-quantification device.
But if I had to choose my favorite all-encompassing, easy-to-use device for individual use and measurement of just about anything you'd every want to measure on your body, at this point, it would definitely be the ŌURA ring. I still do indeed use NatureBeat for about 5 minutes each morning when I wake up because it fills me in on sympathetic vs. parasympathetic nervous system balance, but that's about the only other self-quantification device I regularly use these days.
Before closing, I'll fill you in on two other cool little secrets I just found out from the folks at ŌURA…
…they are going to be rolling out a complete web dashboard next month that allows you to login with a username and password and collect a ton of data that you aren't able to view on the ŌURA smartphone app. If you currently own the ring and are using the app, you're going to be absolutely blown away by all the additional data you're able to have access to when they launch this new web dashboard., including the ability to view long term trends based on day, week, and month breakdowns.
In addition, OURA recognizes that the energy expenditure (Metabolic Equivalents or METs) for certain activities can often not accurately be accounted for by the ring. For this reason, they now support manual data entry for some of the more common activities. You choose the activity, duration and intensity level, and then OURA will add the METs for these activities. You will also have the ability to edit and delete any activities you add. The coolest thing about this, in my opinion, is that if I do decide to take the ring off for some kind of exercise session, or I forget to put it on for a workout, then I can just go back in and manually enter my approximate workout data. Here's what it looks like:
Pretty nifty, eh?
Anyways, that, as of today, is now all fully functional in the app, and if you stay tuned to my blog and subscribe to my free newsletter, you'll to be the first to know when that slick new ŌURA website dashboard is released, and in the meantime, – you can click here to get an ŌURA ring.
Leave your questions, comments and feedback below and I'll be happy to answer!
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- Heart rate variability. Standards of measurement, physiological interpretation, and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and ElectrophysiologyEur Heart J 1996;17(3):354–81.
- Plews DJ, Laursen PB, Stanley J, Kilding AE, Buchheit M. Training adaptation and heart rate variability in elite endurance athletes: opening the door to effective monitoring. Sports Med Auckl NZ 2013;43(9):773–81.
- Schäfer A, Vagedes J. How accurate is pulse rate variability as an estimate of heart rate variability? A review on studies comparing photoplethysmographic technology with an electrocardiogram. Int J Cardiol 2013;166(1):15–29.
- Vesterinen V, Häkkinen K, Hynynen E, Mikkola J, Hokka L, Nummela A. Heart rate variability in prediction of individual adaptation to endurance training in recreational endurance runners. Scand J Med Sci Sports 2013;23(2):171–80.
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- de Zambotti M, Rosas L, Colrain IM, Baker FC. The Sleep of the Ring: Comparison of the ŌURA Sleep Tracker Against Polysomnography. Behav Sleep Med 2017;1–15.