Whoop 4.0 review: a diehard fitness tracker for people who like pushing their limits

Whoop 4.0 review TL;DR: top-tier fitness tracker for athletes who train too hard, too often. The data won’t come cheap, though.

I can’t remember the last time I was as dedicated to wearing a heart rate monitor (which is also a fitness tracker) as I was when I tested the Whoop 4.0. I wore the band day and night and only took it off for when I showered (no one likes a soggy band wrapped around their wrist). I was curious to see how the data stacks up over time and if the Whoop 4.0 can determine my readiness for fitness every day.

From what I can tell, it really can. I’m yet to conclusively determine whether or not the Whoop 4.0 is the most precise fitness tracker in the world but based on a month-long test, heart rate data mostly matches other fitness wearables such as the Polar Verity Sense or the Coros Pace 2.

Should you buy one? Can you even buy a Whoop 4.0 tracker? Let’s find out.

NEWS FLASH! The Whoop 4.0 won the Best Fitness Tracker category at the T3 Awards 2022!

Whoop 4.0 review: Price and availability

The Whoop 4.0 is available now but you can’t buy it outright, only part of the Whoop subscription. Included in the membership cost, you get the Whoop 4.0 for free and access to the Whoop App.

You can sign up at Whoop, membership costs start from $18/£18/AU$18 month. 

Whoop 4.0 review: Design

At first glance, the Whoop 4.0 band comes across as a pretty basic fitness wearable: it’s an optical heart rate sensor unit attached to a band. Of course, the actual technology involved is more complicated than this, but Whoop 4.0 is a straightforward device from a day-to-day wear perspective.

That said, the Whoop 4.0 introduces an upgraded sensor configuration that now features three green, one red and one infrared LEDs (five in total), four photodiodes, and advanced algorithms to improve accuracy and heart rate measurements (more on accuracy in just a bit).

Overall, the new Whoop 4.0 is 33% lighter than the Whoop 3.0. Despite the more lightweight body, the Whoop 4.0 actually improved on battery life thanks to the new Whoop Battery Pack 4.0 technology that uses Sila’s silicon anode battery materials. Battery life is not too shabby (around four days on average), especially considering the fitness band uses an optical heart rate sensor.

Another new thing is the vibration motor that is used for the wake-up alarm. It works well as advertised and is a nice touch, especially considering the emphasis on sleep tracking in the Whoop ecosystem. The Whoop 4.0 can also measure skin temperature, blood oxygen levels, heart rate variability and resting heart rate.

Whoop 4.0 review: Accuracy

Although people liked the Whoop 3.0, it was widely criticised for not being terribly accurate. Thankfully, Whoop addressed this with the new sensor, which based on my experience is considerably more accurate. Only on occasions did the heart rate reading go off the chart; the Whoop 4.0 even performed well during strength workouts which are generally harder to track.

Speaking of workouts: I tested the Whoop 4.0 for a lot of those, mostly strength workouts. I think of the ten or so activities I tracked, only once the Whoop 4.0 lost the plot and said my heart stopped. It was on the ball most of the time, and I could clearly see the rising and falling pattern of my heart rate as I did my sets.

It was struggling a bit when trying to keep up with the peaks and troughs of my heart rate during workouts and after a bigger dip, the Whoop 4.0 seemed to have lost track of the heart rate rhythm. The heart rate averages seemed fine. 

As for tracking runs, I took the Whoop 4.0 out for a couple without the phone to see if I could sync the band with the app afterwards (you can add workouts manually). It was a similar experience as before, and I saw no evidence of heart rate graph anomalies. Admittedly, I didn’t take the Whoop 4.0 for really long runs, but I would imagine it would be able to cope well, as long as the battery is adequately charged.

The Whoop 4.0 also tracks sleep. And since sleep is a fundamental part of recovery, the Whoop system places a big emphasis on monitoring and analysing sleep. Accuracy here was great, too, only on two occasions have I had to manually edit the sleep data (it took me being lazy on the sofa in the evening as sleeping).

Daily sleep statistics are compared to the 30-day average to detect any anomalies. Much like in the case of any other fitness wearables that track sleep, most of the breakdown is absolutely useless as it’s pretty hard to action the lack of REM sleep, for example. However, sleep quality does feed into your Strain Score, which is admittedly the main feature of the Whoop ecosystem.

Whoop 4.0 review: The Whoop App

In the World of Whoop, every single piece of data collected has something to do with strain. Therefore, the most critical part of the Whoop App is your Strain Score. It can be anything between 0-21 and based on your recovery and workload, Whoop will recommend the correct amount of strain for each day.

Just existing every day will increase your Strain Score, but exercising will add to it too (obviously). Each activity has its own Strain Score, but these Activity Strain Scores don't just get piled onto your daily score. A couple of activities with a score of 9-10 won't all of a sudden push your Daily Strain score over 21.

As Whoop explains, strain uses a "non-linear calculation", and the algorithm aggregates your raw data then scale the final results to get your overall strain score.

Keep in mind that just because the Whoop App recommends a certain amount of strain for the day, that doesn't mean you need to go out of your way to meet this strain goal. The Whoop App will assess your body's readiness for action and recommend some exercise, should you want to exercise. It's not an obligation, only a recommendation.

This is not exclusively an issue with Whoop; most fitness wearables follow a similar pattern. Some will go as far as saying you're "detraining" when you don't exercise as much as recommended, resulting in people massively overtraining and injuring themselves.

I use it to look at the Whoop App on the day I was planning on exercising anyway to see how much I can push myself. If my recovery and sleep weren't excellent, I wouldn't try crushing my deadlift or 5K PBs that day. 

Whoop 4.0 review: verdict

The Whoop 4.0 is an excellent fitness tracker but mainly for those who prefer to train hard and would like to know when to slow down a bit. It could also come in handy for people who are generally interested in how well their bodies recover from day to day strain.

I would be surprised, though, if people who are just somewhat interested in their performance are willing to shell out the monthly cost to access their stats. Whoop membership costs can add up over time and even if you're not using the band, you'll still have to pay the monthly fee.

Another danger Whoop face is fitness wearable brands, including Garmin and Fitbit, adding similar features to their ever-increasing feature arsenal, making the market for subscription-based fitness wearables more competitive.

I for one really enjoyed using the Whoop 4.0 band and relished myself in keeping track of my Strain Score. If you’re into fitness and sports, the Whoop 4.0 can help you achieve the optimal balance between rest and workouts. As long as you are happy to pay the price.

Whoop 4.0 review: also consider

The Polar Verity Sense is a fantastically versatile, feature-rich and well-priced heart rate monitoring strap, very similar to the Whoop 4.0 from a physical design perspective. There are no monthly costs but admittedly, the free Polar Flow app is not as user friendly as the Whoop App.

The Fitbit Charge 5 provides you with a Daily Readiness Score which is essentially the same as the Strain Score in the Whoop App. To access it, you need a Fitbit Premium subscription which will also cost you a  monthly fee, just in the case of the Whoop App.

I would also recommend just getting a running watch. The best running watches are versatile fitness wearables that – unlike the Shoop 4.0 – often have GPS. Top-tier running watches can train you to run better, faster and more efficiently; easy as that.