HRV hardware: They all measure the same thing, don’t they?

In our focus series HRV-Insight , the CEO and medical director of Autonom Health GesundheitsbildungsGmbH discusses and documents
Dr. med. Alfred Lohninger will cover various HRV topics, including current HRV research areas.
This time it’s about the difference between smartwatches and sensors with electrodes. With this analysis, we would like to offer you arguments as to how we position our products. This makes it very clear what benefits or additional benefits our products offer compared to the competition and, above all, what unique selling point they have.
This is the best way to advertise them.

Dr. med Alfred Lohninger
Dr. med. Alfred Lohninger

A high HRV stands for a high adaptability, a low HRV indicates stress.

Measurements of heart rate variability (HRV) provide information about the autonomic nervous system and thus provide information about the interplay between parasympathetic and sympathetic activity.

As the topic of HRV is becoming increasingly well-known and interesting, there has been a significant increase in HRV providers in recent years, both in the hardware and software sectors.

Nowadays, every second person wears a smartwatch that also claims to be able to measure HRV. But is that true? And what about data quality? In this article, we will look at the differences between smartwatches, chest straps and sensors with adhesive electrodes.

Back in 2018, we wrote a blog on the topic of “HRV measurements with a chest strap – how good is the data quality compared to an ECG?”. HRV chest strap systems can have excellent data quality and make measurement much easier compared to an HRV recorder with adhesive electrodes.

Beispielhafte Smartwatch

What exactly does a smartwatch measure?

Depending on the model and type, wearables use various sensors to collect data, analyze it and record it for comparison purposes.
Smartwatches are wearables that combine the functions of a cell phone and fitness tracker, e.g. displaying messages, managing appointments, tracking training sessions, but also measuring fitness, heart rate and sleep quality.

Thanks to many technical options, such as a gyroscope sensor that detects rotational movements, an altimeter and a GPS, GLONASS or GALILEO positioning system, a smartwatch can determine whether the user is currently moving or sitting still. Some smartwatches even measure blood pressure, and some can measure blood oxygen and heart rate. They often also have a sleep analysis function that can differentiate between wakefulness, light sleep and deep sleep.

Many smartwatches offer the following features:

Breathing rate: By measuring how often the wearer takes a breath per minute, activity and stress levels can be derived.
Distance: Most modern wearables display the distance covered. This works thanks to GPS positioning and motion sensors.
ECG: Some watches can record ECGs, which are used to draw conclusions about heart health.
Recovery requirements: Some wearables use an index to indicate whether it would be better for the body to train or rest.
Women’s health: This feature can track menstruation days and provides information about energy levels on individual days, general well-being and overall health status.
Heart rate: This value is intended to help you stay in the optimum range during training.
Altimeter: Many sports watches have an integrated barometer. This recognizes differences in air pressure and can therefore detect whether you are walking uphill or climbing stairs, for example. The wearable recognizes how many meters of altitude you have covered.
Intensity: A smartwatch can recognize the intensity of the training. This is read out by a combination of motion and GPS sensors.
Calories: The smartwatch measures the amount of calories burned and calories consumed based on activity, training duration and intensity.
Position/compass/navigation: GPS (“Global Positioning System”), GLONASS (“Global Navigation Satellite System”) and Galileo are the names of the various satellite navigation systems that help to determine your position. Together with the smartphone, the wearer’s current location or movements can be tracked.
Blood oxygen saturation: Sp02 is a value given as a percentage and indicates the estimated oxygen saturation in the blood.
Sleep quality: Based on heart rate, breathing and movements, wearables draw conclusions about which sleep phase we are in and how good or bad our night’s sleep is or was.
Stress/heart rate variability: The Fitbit “Sense” also uses a sensor for electrodermal activity (EDA) to evaluate the stress indication, which measures electrical changes on the surface of the skin.
Training progress: If a fitness watch records data such as exercise, sport, repetitions, distance, speed etc. over several days, weeks and months, these are displayed in the form of diagrams.
Training duration: The time an activity takes is a factor in calculating calorie consumption, training intensity and training progress.

How does a smartwatch measure?

Most devices now rely on optical pulse measurement on the wrist with light sensors or transmit the number of heartbeats to the watch using a chest strap.
If the pulse is measured directly, this is done with two or more LED lamps and an optical sensor on the underside of the housing.

And now things are getting particularly exciting for all HRV professionals, because:
1. the smartwatch values are only displayed as a trend and
2. they do not provide exact results, as they are only measured indirectly by software.

Conclusion: Smartwatches cannot keep up with the accuracy of sensors that receive electrical signals, such as chest straps or recorders with electrodes.
And another not entirely irrelevant side note: light sensors also require a calm posture such as lying or sitting. As soon as you move more, and they are prone to measurement errors!

Can I carry out long-term HRV measurements with a smartwatch?

Can I carry out long-term HRV measurements with a smartwatch?

In general, smartwatches and wrist sensors are designed to measure heart rate and not R-R distances. And it is precisely these R-R intervals – the time spans from heart to heartbeat in milliseconds – that make it possible to measure heart rate variability!

According to a study from February 2021(, there are currently no smartwatches that are capable of 24-hour recording:
“Heart rate variability (HRV) measurements provide information about the autonomic nervous system and the balance between parasympathetic and sympathetic activity. A high HRV can be beneficial and reflect the adaptability of the autonomic nervous system, while a low HRV can indicate fatigue, overtraining or health problems.
There has been an increase in wearable devices that claim to measure HRV. Some of these include point measurements, while others only record during rest and/or sleep phases. Only a few are able to measure HRV continuously (≥24 h). We conducted a narrative literature review to determine which currently available wearable devices are capable of continuous, accurate HRV measurements. The review also aims to assess which devices would be suitable in a field environment specific to military populations.
The Polar H10 appears to be the most accurate wearable device when measured with criteria, and even seems to replace traditional methods during exercise. However, the H10 currently needs to be paired with a watch to extract the raw data for HRV analysis if users need to avoid using an app (for security or data ownership reasons), which incurs additional costs.”

One of the providers that sell long-term measurements is WHOOP.
This Boston-based technology company works with a bracelet that can be worn continuously. However, WHOOP does not report any recognized HRV values, but works with its own values, the calculation of which is not disclosed.

Wearable Devices Suitable for Monitoring Twenty Four Hour Heart Rate Variability in Military Populations.
Fig. 2: Wearable Devices Suitable for Monitoring Twenty Four Hour Heart Rate Variability in Military Populations. Source:

Why long-term measurements?

“Because you can understand relationships much better with a long-term measurement!”

That was the spontaneous reaction of our employee Lorenz Pühringer to this question. And he immediately provided some self-evident examples:

An example
I go running in the morning and overexert myself. As a result, my body is overloaded and can’t cope with the stress of work. So I’m exhausted and tired all day. But if I took a 5-minute measurement in the morning before my run – many smartwatch providers recommend taking measurements after getting up – the watch might tell me that I’m fit. In contrast, with a long-term measurement I can track the course of various things.

Example of sleep measurement and sleep quality
Many watches measure sleep quality. If I have had a bad night’s sleep, the watch gives me some values, but cannot tell me why they are bad. But with a 24-hour measurement, this is certainly possible. I can also see in the spectrogram exactly when my sleep was good and when it was rather poor.
And there’s more: fatty, unhealthy food in the evening from around 6 p.m. is usually heavy on the stomach. The body has to work long and hard to digest this food. And if I go to sleep in the middle of this digestive process, my sleep will certainly be worse than if I had eaten something easier to digest or even earlier.

Coaching and support
Another very important point is the feedback and support based on the measurement data.

We at Autonom Health are one of the few companies that offer coaching for HRV measurements. This is also very important, because HRV is an area that has many facets and it is only possible to get the full potential out of HRV measurements with a lot of experience and expertise. Most users find this too complicated and time-consuming. And this is exactly where the possibility of coaching is an advantage.
Only HRV measurement with a chest strap and professional evaluation provides this enormous added value!

Smartwatches are less accurate due to the sensors used and cannot take long-term measurements. However, long-term measurements are precisely the decisive factor in HRV. Because they provide fundamental insights into the health status of the person being measured!

However, smartwatches definitely have their place! Especially for people who want to familiarize themselves with their health in a playful way without investing a lot of time.
However, when it comes to precise findings and lifestyle changes, for example due to burnout, it is better to use a precise sensor and sophisticated software.

Frau legt Brustgurt an
Fig.3: Autonom Health chest strap (Source: Autonom Health)

When is the smartwatch useful, when is the 24-hour HRV measurement useful?

Smartwatches, life trackers and wearables have undergone rapid development as a result of the current fitness movement. A wide range of vital data can be recorded with these devices. This in turn gives the user a large number of evaluations.

However, the question is: how big, how simple and how reliable is the use of this data and, above all, how valid are the results?

About the limits of smartwatches
There are relatively large fluctuations when recording vital data using wearables or smartphones. Most wearables detect heart rate and other factors by directing a beam of light at the wrist and then determining how much light is absorbed. Greater light absorption indicates a greater volume of blood flowing through the veins under the skin. However, this method has a wide range of variation, depending on the current activity level, skin thickness and skin color.
There is also a major lack of interoperability and standardization. Manufacturers often define the analysis values themselves. They are hardly standardized. Standardized and open interfaces are a necessary feature of wearables for use in mHealth applications. This stands
However, this is contrary to the interests of most manufacturers of such devices.
And finally, many smartwatches also raise the question of data protection and data security.
What happens to the collected data? Where are they stored? Who has access to it?
What everyone should know: Data protection and data security are unfortunately still a blind spot when it comes to wearables. Many manufacturers even use the collected data for advertising purposes without consulting the customer.

HRV by Autonom Health

The measurement of HRV is a reliable and highly sensitive screening instrument that can be used to determine a person’s general state of health.
Autonom Health’s HRV analyses comply with all required HRV standards and meet the guidelines for performing and analyzing HRV measurements established in 1996 by the Task Force of the European Society of Cardiology (ESC) and the North American Society of Pacing and Electrophysiology (NASPE).
In the area of data security, we comply with the IT security guidelines, which also meet the requirements of the EU Data Protection Regulation and the Network and Information Security Directive.

The most important health parameters are precisely measured and analyzed:

1. state of health: Describes the “functional efficiency” of the entire organism, the current constitution, performance and regeneration capacity.
2 Current biological age: Heart rate variability correlates with health and age. The functional current biological age therefore measures the current ability to adapt to changing external and internal conditions.
3. performance potential: the level and dynamic progression of cardiac output and HRV data in comparison to one’s own age and gender group reflect the current level of physical and mental performance.
4. stress processing: Vegetative resilience describes the ability to deal productively with stress and strain and still regenerate well.
5. burnout resistance: The value measures resistance to stress. The lower the biological age, the more adequate the physiological patterns during activation and rest, the better the physical and mental performance and sleep, the higher the burnout resistance.
6. sleep: The exact quality of sleep (fatigue sleep, suspected snoring, poor, medium, good, very good) in your own bed is calculated to the nearest 5 minutes.
7. regeneration: the number, timing, duration and quality (decrease in heart rate and sympathetic activity, increase in parasympathetic tone) of regeneration phases are evaluated.
8. mental performance: complex algorithms calculate the degree of focus, physical tension and economy (from exhaustion or fatigue to flow) during mental performance.
9. physical performance: heart and HRV performance data calculate the target range, effectiveness during and regeneration after physical exertion.
10. nutritional behavior: The number and duration of meals and breaks between meals, in combination with the individual energy level during and after eating, enable current reflection on personal eating habits.
11. peer group comparisons: All results, cardiac output and HRV data in graphical and numerical comparison to age and gender group.
12.recommendations: Specific individual recommendations based on the current measurement results for the targeted optimization of health.

read more:

Scroll to Top
Cookie Consent with Real Cookie Banner