2021 has been the year of wearable technology for me with the task of testing out at least 25 wearables and it is difficult for me to settle in on just a single one to fully satisfy me. For the past three months, I have been testing out the newWhoop 4.0  and despite not having a display I find the device to be more useful to me than the new Oura Ring 3.

Watches have been mounted on my left wrist for most of my life and I appreciate the ability to glance down to check the time and date. Watches have evolved over the past twenty years since I've been covering mobile technology with some smartwatches able to provide functions found in phones just a couple of years ago. At first glance, the Whoop 4.0 seems to be a step back with no display at all. However, the power and usefulness of the device is found in the analysis and presentation of the data to help you understand your body and its current state of readiness.

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My Whoop 4.0 review kicked off with a rocky start due to a defective sensor unit and battery pack that charged the device up at a rate of about 2% per hour and also died after a day. For some reason, that unit also kept disconnecting itself from my phone and I had to pair it back up every other day with a limited amount of data collected. I was so frustrated with the experience that I was ready to send it back, but I saw others enjoying the device so knew there was clearly something wrong with that particular unit.

Whoop 4.0

4.5/ 5 Very good

pros and cons

Pros

• Very comfortable for 24/7 wear
• Detailed sleep tracking
• Informative coaching
• Unique battery pack system
• Affordable
• Useful clothing options

Cons

• Battery life could be longer
• No support for importing GPS data

$180 at Whoop

After a replacement arrived, things have been going well with the battery pack charging up the sensor in connected and mobile modes, the Whoop 4.0 lasting for four to five days, and data syncing perfectly. I've been wearing the WHOOP 4.0 on my right wrist, and in the band of the boxers (more on this later), since I need to have a watch with a visible face on my left wrist. This works out just fine as the Whoop 4.0 provides key extended wear information while the watch on the left wrist switches out weekly to try something else for a review. I'm almost settled on one or two-star watches, but there is overlap in the data collected with some watches and the Whoop 4.0 so I'm still working through evaluating the optimal setup for me.

I love the extremely long battery life, training plans, Training Hub, and nearly everything else about my newCOROS Vertix 2 and since it is quite weak in the area of sleep tracking (not to mention it will knock my wife out if I roll over in bed and my arm strikes her head) I take the watch off while I sleep and let the Whoop 4.0 handle the details of tracking my sleep. It would be great to see a bit more synchronization between the Whoop 4.0 and some other services, but I may be asking too much between competitors.

Also:COROS Vertix 2 outdoor sports watch review

Hardware

The Whoop 4.0 hardware itself is a small black rectangle that houses the battery and five LEDs (three green, one red, and one infrared) to measure your various body processes. Whoop states that it is 33% smaller than the Whoop 3.0 and I never tested that so we'll trust that metric. It is waterproof up to 10 meters and offers four to five-day battery life.

There are two grooves on one side where the strap slides into place (a system called Fast Link) while the other end has two holes on either side to mount the other end of the strap with two pegs on the strap side. The sensors are found on the bottom with a plain black plastic top. It's a rather unremarkable piece of hardware when you look at it.

There is an indicator light on one side of the Whoop that shows you different color lights for charging, Bluetooth pairing, and more.

A small thicker block of black plastic slides down and onto the Whoop device and serves to wireless charge it up. The battery pack has a USB-C port on one side to charge it up with a very small USB-A to USB-C cable included in the retail package. The greatest aspect of this battery pack is that you can connect it while wearing the Whoop 4.0 on your wrist so you can charge up the Whoop and keep on tracking your data. The battery pack is even waterproof in case you happen to be outside in the rain or something, but I certainly wouldn't go swimming with it on as it could still slide off. Extra battery packs are available for$49 too.

A SuperKnit black band was included with the Whoop 4.0 package while Whoop also sent along a light blue, Ice, color SuperKnit 4.0 band to also test out. There are a large number of available colors, priced at$49 each. Whoop also offers a bicep band for$54 and higher-end SuperKnit Luxe bands for$99 each.

Whoop also uses its Any-Wear technology to provide data collection with Whoop Body gear. This gear includes sports bras, compression tops, leggings, shorts, athletic boxers, bralettes, and everyday boxes. I tried a pair ofAny-Wear Boxers  but did not include any photos of them in this review. The Any-Wear gear ranges in price from$34 to$109 with some training packs available that can save you 15% on the combination.

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See also: Best smartwatch: Apple Watch and more top picks.

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WHOOP smartphone app

Since the Whoop 4.0 has no display, you rely upon the smartphone application to setup, manage, sync, view, report, and fully experience your Whoop. It is available for both iOS and Android and for this review I used the lovely large display of myZ Fold 3  to interact with the Whoop data that was captured by the device.

At first, I thought the Whoop was just an advanced sleep-tracking device that offered more than my GPS sports watches, but it's more than that. It does track the details of your sleep but is also measuring other key metrics of your body throughout the day. One key metric that is important to Whoop is strain and this is defined as the measure of your cardiovascular load, scored on a scale of 0 to 21. Four categories of strain; light, moderate, strenuous, and all-out, are provided by the Whoop. Even if you are active throughout the day, you could end up with light strain if all of that time was casual walking around. Individual workouts receive strain scores, but there is also a day strain that looks at your body for the entire day and night. Strain is a measure of your heart rate so the longer time you spend in higher heart rate zones then the higher your strain will be.

When you launch the Whoop app you will be taken to an overview screen and then you can swipe through to view strain, recovery, and sleep data. Moving down the screen shows you your data over a week-long period. You can also then tap on the bottom buttons to view more details of your data. This includes heart rate variability, resting heart rate, respiratory rate, sleep details, and more with a 7-day average as a comparison.

On the overview screen, tapping on sleep takes you into a detailed plot with minute-by-minute sleep tracking heart rate data and summary information. There are some words that describe your night's sleep so it helps you understand the data presented to you in such detail.

One interesting aspect of the Whoop system is the journaling feature. There are a ton of available questions and you walk through the setup to select questions that are applicable to your situation and then on a daily basis, the questions appear so you can quickly log your day and night. Over time, the journal will feed into your reports and provide you with a detailed picture of factors that influenced your sleep or performance.

The second tab over in the software is the coaching page that provides sections for strain coach, sleep coach, health monitor, and then weekly/monthly performance assessments. The health monitor is one of my favorite features and tapping on it opens up real-time heart rate tracking, along with the details of your last evening's sleep. The data include respiratory rate, resting heart rate, skin temperature, blood oxygen saturation, and heart rate variability. You can then even share your health report as a PDF document with your coach, doctor, or other interested parties.

The Whoop application can also be used to track your activity from your phone, in combination with the Whoop 4.0 tracking your heart rate. Since I'm using a big Z Fold 3, I have not yet tested this capability and will have to swap my SIM over to a smaller phone I can run with to test this out. There are communities and teams you can join to share your key data and help motivate you to improve. The last tab is where you manage your membership, purchase Whoop gear, and manage your device. Whoop has limited integrations and the ability to share the data outside of the application, but Strava and Training Peaks are supported.

If you want to check out an extremely detailed review of the Whoop 4.0, then I highly recommend you check out Ray Maker's excellent review as he sets the gold standard for wearable reviews and covers the Whoop 4.0 in nearly infinite detail.

WHOOP web application

While the smartphone app is excellent and I have a big screen phone to view it, you should also know that you can review some of your key data using the Whoop web application. One cool feature is the ability to quickly view your data trends as far as six months back.

The web application also shows you some information that is not currently in the smartphone application, such as daily sleep consistency and the trend views of individual sleep stages. Weekly and monthly assessments are easy to read in the web application and can also be easily printed to share.

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See also: Samsung Galaxy Watch 3: Finally, a great smartwatch from someone other than Apple.

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Whoop 4.0 review: in pictures

Daily usage experiences and conclusions

The Whoop 4.0 is extremely comfortable and I don't even think about it sitting on my right wrist with the band. The Any-Wear boxers are comfortable and offer a nice alternative to mounting the Whoop when I want to test out other watches, don't feel like wearing something on both wrists, or want to sleep without anything on my wrists. I was pleasantly surprised by how well the Whoop still tracked my sleep and activity details while in the band of the boxers and will definitely consider other Any-Wear gear too.

The Whoop is supposed to automatically detect activities when you experience heart rate elevation for more than 15 minutes, but I didn't see this happen on a regular basis. My typical scenario was to go back in and manually add my activity, using my GPS sports watch details, after I completed the activity and then a plot of my heart rate and other basic stats appeared. If you use your phone to capture the data during an activity then the experience might be more reliable. I would like to see the ability to have GPS data imported into Whoop to include in the strain calculations for my day.

I really appreciate the alarm system on the Whoop 4.0 since I wear it to be every evening. You can set to have your alarm go off at an exact time, once you hit your sleep goal, or once you've achieved a green recovery. One of the best things about the Whoop system is the sleep coach that also informs you when you should go to bed and if you miss that then it will provide real-time information on how much of your sleep need you are likely to reach if you go to bed now.

One thing that commonly derails athletes is injury and the Whoop 4.0 is designed to help you understand your body's ability to perform and your recovery status. Whoop has an interesting article on why runners should consider a Whoop, even if they happen to wear a GPS sports watches for real-time run tracking and metric tracking.

The Whoop 4.0 hardware is available now and it is free. However, you must sign up for a membership with the shortest period of six months at a price of$30 per month. Thus, six months of service and the Whoop 4.0 will cost you$180. You can sign up for an annual membership for$288 ($24/month) or an 18-month membership for$324 ($18/month). While some people may not like a membership model, the overall cost of the service and the device is reasonable for a wearable that provides such advanced and detailed data capture, coaching, and reporting capability. I'm definitely signing up for membership now that my review is done and look forward to continuing to analyze my data and improve my health and wellness.

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