It has a peculiar name – WHOOP, and they don't call it a band but rather a "strap". However, this device is a serious contender in the fitness wearable market. It captures highly-detailed sleep and heart rate data, along with something new: heart rate variability.

To purchase the WHOOP Strap you must buy a monthly membership rather than the device itself. It's a unique revenue model and it's expensive, clocking in at $30/month although deals are available if you buy longer membership plans. A credit towards your membership is also available.

Cost of membership at time of writing (late 2019)

What makes WHOOP different

With its higher price tag comes a few differences compared to your typical fitness tracker. In general, the WHOOP is marketed towards high-performance athletes, although this may also serve as a clever marketing strategy. After all, if it's good enough for an athlete, surely it can help me reach my goals?

User experience

The biggest difference from a user perspective is that WHOOP will give you a daily score of your recovery and strain. Based on this information you are supposed to make decisions about your training and activity. I haven't seen other popular fitness trackers, like the Fitbit, give scores like this.

The strap itself is waterproof and intended to never be taken off. All of its sensors measure data continuously. Therefore it is extremely accurate at measuring sleep start and end times, and sleep stages.

The goal, according to WHOOP, is to "provide athletes with an unprecedented amount of insight into how their bodies are adapting to training programs, the sufficiency and efficiency of their sleep, and more broadly, how well their body is adapting to environmental demands."[1]

Hardware

To calculate all this data the WHOOP Strap includes an accelerometer and measures your heart rate, temperature, and skin conductivity.[1] None of that is very unique in the fitness world, but in fact, their heart rate sensor is fast enough to calculate something called heart rate variability (HRV), a metric quickly becoming essential for athletes because it can give insight into whether your body is properly recovered or not.

Put simply, HRV is a measure of the beat-to-beat fluctuations in your heart rate. If you have a heart rate of 60 beats per minute it doesn't mean your heart is beating exactly once per second. Some beats might be 0.9 seconds apart while others might be 1.1 seconds apart.

These variations in heartbeat timing are controlled by your nervous system and are constantly fluctuating throughout the day. Trends in HRV can help determine how stressed your nervous system is, whether you're starting to get sick, and if you need to rest more after a hard workout day.

Why measure HRV

HRV can indicate the state of your autonomic nervous system – the unconscious system that regulates heart rate, digestion, respiratory rate, urination, sexual arousal, and other bodily functions.

When there is less variation between heartbeats (lower HRV) it indicates that your nervous system is in a sympathetic or "fight-or-flight" mode. More variability between heartbeats (higher HRV) indicates that your body is in a parasympathetic "rest-and-digest" mode.

Neither state is purely good or bad and everybody's HRV is fluctuating throughout the day, but patterns can indicate the general state of your nervous system. For more information about HRV, I've written a separate article about what heart rate variability is and why it's important.

WHOOP first impressions

At first, the nylon strap on the WHOOP seemed a bit flimsy and cheap. However, it has turned out to be the most comfortable band I've ever worn. Much more comfortable than a Jawbone, Fitbit, or watch. I often forget it's there and it doesn't bother me when I sleep.

I'm impressed by the overall product design and attention to detail. The device hugs your wrist so that the light from the green heart-rate LEDs don't leak out the side, a problem I often had with my Fitbit.

The device is waterproof and it has performed well in every environment I've tested it in, including the pool, shower, and sauna. In my experience, WHOOP has truly built a device that you can wear 24/7.

Clever engineering on their battery charger, which slides over the strap and charges while you're still wearing the device. Very bright battery indicator.

Mobile app

Overall, the mobile app is underwhelming. One serious issue is that several features appear to be missing from Android devices at this time.

The UX is clunky and it's hard to see real-time data. Some simple metrics, like being able to see heart rate and HRV in real-time are not available.

Every morning after you wake up there is an input screen for questions like "How tired are you?" and "How sore are you?" but you only have one chance to answer them and you can't change your answer after it's submitted. Also, it's not clear how this data is being used and you can't see trends over time.

You can't see the number of steps you've taken, a metric that almost every other fitness device out there gives you. While steps is a limited measure, it's useful in one specific regard – it gives you a sense of how much you've moved. No other metric on the WHOOP gives you such a direct reading of the accelerometer like the number of steps does.

I personally don't like the color scheme. I find it dark and depressing, but then again I'm a big fan of light/bright color schemes in general.

Heart rate issue

Unfortunately, despite the high-quality sensors in this device, the WHOOP doesn't reliably measure heart rate. As you can see below it's easy to trick the device simply by swinging your arm.

After discovering this issue I contacted support and they sent me a bicep band, which I appreciate. However, if the device requires a bicep band to operate properly I think it should come for free with every device.

To be fair, the heart rate does seem to be accurate in other scenarios when the arms aren't moving as much, and I'm sure WHOOP will continue to improve their algorithm.

User data is not available

The WHOOP Strap collects a huge amount of user data, but none of it is currently available for download by the user.

According to Will Ahmed, the CEO of WHOOP, they're working on allowing users to export their data. However, this is 2019 and any fitness wearable company should have data export features out of the box. WHOOP has been around for several years so it's unacceptable that a tool doesn't exist yet.

Working on it — Will Ahmed (@willahmed) May 15, 2019

Data extract workaround

Out of frustration, I built my own tool – to extract your data head on over to HabitDash.com. This will export your raw data in JSON and CSV format so that it can be opened in any spreadsheet editor.

I hope this workaround will be replaced as soon as possible by an official feature from WHOOP.

WHOOP wish list

The ability to export your user data. The days of closed systems need to be in the past. Give me my data!

Improvements to user experience. Every time you wake up in the morning you are asked several questions about your sleep. The questions are phrased negatively so you have to select "X" to each one, as in "that didn't apply". It's confusing. Questions should be phrased so that a positive checkbox is the default.

The ability to edit user feedback on sleep and recovery. Currently, once you input the answers you can't change them.

Steps metric. As mentioned above, number of steps is a useful metric to determine how much you've moved. No other measure provided by WHOOP (including strain) gives a direct estimate of movement.

A light theme for mobile. The mobile app is too dark in my opinion.

User forum to discuss the product and talk about improvements.

Final thoughts

Overall, I'm very impressed with the WHOOP Strap and right now it's my fitness tracker of choice. I use it every day to track my sleep and log workouts. The device and its charging mechanism are unique and clever. However, the mobile app experience needs to be improved badly, and more data needs to be made accessible to the user.

I recommend joining the WHOOP Athletes Facebook group which currently has several thousand members. It's a good forum to discuss questions and issues.

If you want to learn more about the device, go to the WHOOP website. I'm excited to see what this company comes up with in the future and what kind of competition will occur in this space.