Whoop 4.0 review: Can a subscription-based fitness tracker work?

NextPit Whoop 4 0 Review
© NextPit

The Whoop 4.0 does pretty much everything differently than ordinary fitness trackers - and is actually much more of a fitness tracker than all the Fitbit Charges and Honor Bands out there, which are now rather slim smartwatches. Why the Whoop 4.0 is different in so many ways and whether the concept works out, you can read in the review below.



  • Can be worn in a variety of ways
  • Comprehensive analysis functions
  • No display


  • Does not support chest straps
  • Long-term expensive subscription model
  • No display

Whoop 4.0 in a nutshell

Essentially, the Whoop 4.0 answers two questions: Are you exercising right? And are you recovering properly? Here, as there, you get a quantified answer to help you push yourself and recover to the right degree. The Whoop clearly articulates the claims using simple parameters and clear charts in the app.

However, these demands are huge. If you don't get much exercise at work, you'll have to work hard in your free time to reach your exercise goals. Three hours of intense exercise with over 1200 calories burned? 13.9 out of 21 points! And the sleep goals of sometimes more than ten hours are also impossible for me to meet - at least during the week. I certainly don't go to bed at 8:30 p.m. voluntarily.

Whoop 4.0
The Whoop 4.0 is exceptionally comfortable to wear with the fabric wristbands / © NextPit

Even aside from these very clearly stated goals, the Whoop 4.0 does a lot of things differently. Instead of buying it, you subscribe to the tracker - all you can buy are all kinds of "attachments" to your body, from sports bras to compression shirts. The subscription costs 30 dollars per month if you pay monthly. In the annual membership, you pay $25 per month, in the two-year subscription, it is still $20 per month - so a handsome 480 dollars. But you'll always get the latest model, as long as your contract runs for at least another six months.

Design & operation

The Whoop 4.0 is a fitness tracker - and really only that. There are (practically) no notifications, no music control, and not even a display for the time. But the tracker has other strengths - and thanks to the flexible accessory system, the tracker can be attached to the body more flexibly than almost any other.

What I liked:

  • Chic design with many options.
  • High-quality, robust workmanship.
  • Comfortable to wear 24/7.

What I didn't like:

  • Light fabric wristbands are hard to clean.

The actual Whoop tracker is about the size of a postage stamp and about half an inch thick. There are attachment points on both sides of the tracker for the manufacturer's accessory kit. The wristbands can be swapped in a few seconds. On a positive note, the tracker is completely protected by the wristband and clasp when worn on the wrist.

Whoop 4.0
On the wrist, the Whoop 4.0 is completely wrapped in the wristband and clasp and thus well protected / © NextPit

Included is a black wristband, which you can use to attach the tracker to your wrist. You can get numerous stylish wristband alternatives between $40 and $99. We also tested the Ice (light blue) and Arctic (white) versions, which look really chic. However, keep in mind that the light-colored straps will suffer over time if you like to dig in dust and mud.

This is where the alternative wearing solutions come in handy. The wristbands, for example, are also available in a longer version so that you can wear the tracker on your upper arm. This is not only practical if you often get your hands dirty, but also for sports that put a lot of strain on the wrists. When doing push-ups and the like, the accuracy of the optical pulse measurement often suffers at the wrist, as the blood flow at the wrist is no longer unhindered.

Whoop 4.0
The Whoop 4.0's wristband doesn't stay this pristine for long / © NextPit

There's not much to say about the operation itself. The fitness tracker really only does what the name promises - namely tracking. There is no display, so you have to do without functions like notifications, music control, etc. - or rather, you can, because you have complete peace and quiet. The only interaction is that the tracker lights up your wrist with a double tap. Green means more than 50 percent battery, while orange and red mean that the battery is running low.

Finally, a vibration motor is integrated into the casing. Its only task is to wake you up, either at a set time or with the help of the so-called Sleep Coach within a period that matches your sleep phases as closely as possible. Since I voluntarily don't give up a minute of my sleep, I only tested the sleep phase alarm once - it works anyway.

Whoop 4.0
On the left above the pulse sensor, you can see the LED that shows the battery level on your wrist / © NextPit

Tracking & Sensors

The Whoop 4.0 offers a compelling array of sensors and condenses the data into two primary metrics: Exertion and Recovery, which you can then use to get specific recommendations for your workout.

What I liked:

  • Successful and accurate tracking functions.
  • Long-term tracking and comprehensive evaluations.

What I didn't like:

  • Few options for correlating data.
  • Closed ecosystem.

The Whoop 4.0 has an optical sensor on the bottom with a total of five LEDs: three green, one red and one infrared. Four photodiodes analyze the reflected light and thus determine heart rate, heart rate variability and blood oxygen saturation. The manufacturer also installs a thermometer for the skin temperature in the Whoop 4.0. The tracker generates two values from all this data that will determine your life from now on - or at least dominate the app: Strain and Recovery.

Whoop 4.0 Screenshots
The Whoop app displays the most important data at the top level. By swiping to the left or right, you can switch between the different views / © NextPit

Strain: Load strictly according to pulse

With the strain value, the Whoop 4.0 determines how much you are exerting yourself. Only the data from the pulse sensor over the course of the day is decisive for this. So whether you're doing HIIT workouts or dragging patio tiles around, every activity increases your score. It starts at zero in the morning, and the algorithm's maximum value is 21.

This measurement method has advantages and disadvantages. The advantage is that your individual workload is actually recorded. After all, a 10-kilometer run at 5 minutes per kilometer is a recovery run for a marathon runner, but an impossibility for the untrained. The evaluation is based on how strenuous something is for your personal cardiovascular system.

Whoop 4.0 Screenshots
If you swipe down on the different screens, you will see more details about the course over time / © NextPit

On the other hand, I didn't necessarily find the measured workload to be consistent with the perceived workload. A morning strength workout, for example, had short but extremely strenuous periods of high heart rate. Although I really felt run over afterward, the load measured by the Whoop 4.0 was rather low at "9.3". The relaxed 20-minute run during the lunch break afterwards came in at "11.9," but felt much less demanding. Both workouts together plus sitting around at the desk and on the couch then resulted in a daily load of 14.2, by the way.

The heart rate measurement itself is pleasantly accurate. During the run just mentioned, the Whoop 4.0 measured a maximum pulse of 172 and an average pulse of 159 beats per minute. With a Garmin chest strap, I got exactly the same values as a second opinion. However, things look a bit different during strength training. During a shoulder and arm session, I got an average of 122 and a maximum of 158 beats per minute with the Whoop 4.0. The chest strap indicated a maximum of 165 and an average of 126 beats per minute.

In addition to the measurement for the Whoop app itself, you can also use the Whoop 4.0 as a heart rate sensor for other apps. To do so, simply activate the heart rate broadcast in the settings. On the other hand, it is unfortunately not possible to connect third-party chest straps with Whoop. This is a pity since only Fitbit among the big fitness gadget manufacturers is so isolated in regards to ecosystem.

Whoop 4.0 Screenshots
The heart rate sensors do a good job, but it is best to wear the tracker in such a way that it does not register the heart rate on any part of the body that is currently under extreme strain. This applies to all optical pulse sensors, by the way / © NextPit

Recovery as a complex factor

The second major area of Whoop concerns recovery. The so-called recovery factor indicates how fresh you are on a scale from zero to 100 percent. The relevant factors here are heart rate variability, daily resting pulse, breathing rate and hours slept. The higher this value, the more you can exert yourself.

Whether the value is called "Body Battery" (Garmin), "Daily Readiness" (Fitbit), or "Recovery" - at least for me personally, I have certain doubts about its usefulness. If you do sports, you know your body and can judge how much strain is sensible. I find the Health Monitor, on the other hand, more helpful, and I'll come back to it in more detail in a few paragraphs.

I find it an interesting option to log certain behaviors. For example, you can set up a questionnaire in the app, which Whoop then asks every day when you first open the app. For example, how many grams of protein you consumed, whether you drank alcohol, had sex, supplemented creatine, and so on. However, I find it a shame that there is still no analysis option to relate these logged behaviors to performance. It would be interesting for me to know: Does the glass of red wine in the evening have an impact on my heart rate variability or performance in the morning?

Whoop 4.0 Screenshots
If you train hard, you need a lot of sleep. A lot, says Whoop / © NextPit

Sleep: Whoop the Groundhog

Finally, Whoop 4.0 tracks your sleep. In the test, the times you fell asleep and woke up matched both my memories and the values from the Garmin Epix 2 and Garmin Fenix 7, which I alternately wore alongside the Whoop. Insights into the different sleep phases are not provided by the Whoop app, although I often find these values dubious anyway, as they often give the user little room for concrete improvement.

Nevertheless, the Whoop 4.0 generates a percentage value for sleep performance. This is calculated quite simply as the ratio between hours slept and the sleep requirement determined by Whoop. However, the sleep requirement is hardly achievable for me - the value is often over ten hours. Since my alarm usually goes off between 6 and 7, I would have to go to bed between 8 and 9 pm - not gonna happen. Accordingly, my Sleep Performance Score fluctuates between 50 and 75 percent.

Health Monitor with skin temperature and SpO2

An interesting feature is the Health Monitor in the app. This monitors breathing rate, oxygen saturation, resting pulse, heart rate variability and skin temperature. If one of the values breaks down, you will receive a warning. This can be quite useful in practice. For example, if you start an extremely strenuous workout while your skin or body temperature is elevated, you may be hit harder by an incoming infection. By the way, you can export the data from the Health Monitor as a PDF - as well as weekly or monthly performance summaries.

Whoop 4.0 Screenshots
The Health Monitor on the home screen shows you at a glance: Everything is in the green zone. If this is not the case, you will receive a warning via push notification. This happened to me once because I pulled the tracker off my wrist while I was half asleep and put it on the nightstand. Accordingly, the readings were rubbish / © NextPit

Battery life: charging in a different way

With just under a week, the battery life of the Whoop 4.0 is convincing. I also find Whoop's innovative charging concept very practical, which allows you to never take the tracker off.

What I liked:

  • Decent battery life
  • Smart charging concept

What I didn't like:

  • No notification when the battery is fully charged

Whether in bed, during sports, in the shower, or in the sauna: Ideally, you should wear the Whoop 4.0 24 hours a day for seamless tracking. Accordingly, the manufacturer has come up with a charging concept that allows you to wear the tracker even while it is charging. To recharge, you slide a small power bank on top of the tracker.

Whoop 4.0
The battery pack holds well on the Whoop 4.0 and does not interfere with everyday use / © NextPit

The charging process takes about two hours - and it takes the same amount of time to charge the Battery Pack via the integrated USB-C port. By the way, not only the Whoop 4.0, but also the Battery Pack is water-resistant. However, I did not dare to take a shower with the charging module attached during the test period. However, I was not afraid of splashing water when washing my hands.

The battery life in the test was about five days. You receive a notification via the app when 20 percent of the battery is left - that is, about one day before the end. As mentioned at the beginning, you can also check the battery status via a double tap on the casing. Unfortunately, the only way to see whether the battery is fully charged is to look into the app. The LED on the Whoop 4.0 turns green when it reaches 50%.

Whoop 4.0
The Battery Pack itself is charged via a USB-C port / © NextPit

The LED on the top of the Charging Pack also puzzles me a bit. It glows green when you slide the power bank onto the Whoop 4.0, as long as it has power left to charge. However, the Battery Pack does not reveal how much that is. There is also no way to check the charge status, for example by double-tapping the case. But something has to be left for the Whoop 5.0.

Final verdict

After just over a month with the Whoop 4.0, I've generated countless exciting data about my workouts and sleep patterns, which I can admire in detailed PDFs. However, one question often remains somewhat unanswered: What do I do with this data?

Yes, the Whoop 4.0 gives me specific recommendations like: "Go to bed at 8:45 p.m. today" or "Train today with a load of 12.9 for an optimal workout." But what I'm still missing is a big picture view - and more ways to correlate the data I'm collecting. How does creatine affect my workouts? How does alcohol affect my sleep? Do I train better in the morning, at noon, or in the evening?

The raw data for this would theoretically be available, but my virtual coach doesn't have any really smart advice in store yet. However, this is not a specific Whoop problem, but an unfulfilled promise of the entire fitness gadget industry. Collecting data is no problem. But drawing the right conclusions from it remains a challenge.

The bottom line is that the Whoop 4.0 has a fairly narrowly defined range of functions and doesn't try to be a jack of all trades. And what the tracker is supposed to do, it does really well. However, you also have to consider that there are full-fledged sports smartwatches for the $480 spent on the two-year subscription, for example, the Garmin Venu 2 Plus.


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Stefan Möllenhoff

Stefan Möllenhoff

Stefan gathered his first tech journalism experiences in 2004 – and works in this field full-time since 2008. His enthusiasm for everything digital started already in the 80s with a Sharp MZ700. The smartphone enlightenment came 2002 with a Symbian IRC client for his Nokia 7650. Currently, Stefan is sometimes behind the camera, sometimes writing but mainly taking care of organisational aspects at NextPit. Leisure time consists of cooking, fitness, bouldering, running and everything that has to do with AI and the concept of a Singularity.

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