Published on March 20, 2017
These days, everyone and their friggin’ mother wears a fitness tracker. I’m serious: from old men at golf clubs to soccer moms in mini-vans, it really seems almost everybody has something strapped on their wrist, their arm, their finger, their toes and goodness knows where else – quantifying steps, food, sleep, heart rate and – with each new darling added to the self-quantification wearable market – oh, so much more.
As a matter of fact, according to research firm Gartner, 70 million fitness wearables were sold across the globe in 2015, and sales were projected to grow 18.4% in 2016. That’s a crapload of wearables scuttling around the streets of your neighborhood.
So how the heck does a wearable stand out in this saturated market?
First, it kinda helps to have celebrity endorsements from NBA stars LeBron James and Kyle Lowry and Olympic swimming gold medalists Michael Phelps and Ryan Lochte.
Second, it helps to use state of the art technology and private metrics coming out of Harvard’s Innovation Lab.
And third, you give it a name like “WHOOP”.
In my recent podcast episode with WHOOP Founder and CEO, Will Ahmed, called WHOOP: The Performance Enhancing Wearable That Tells You When To Sleep, How To Exercise, Your Strain Levels & More, Will explains the background behind the name WHOOP by saying “we wanted a name that was energetic, that made people smile. In college, people would talk about sort of their different WHOOP levels in terms of how prepared they felt for the day or for the night.”
So will this thing actually make you smile? Make you energetic? Give you something to talk about at your next college or cocktail party?
Over the past month, my personal assistant Ashley (yes, the same infamous girl who invented these bomb protein recovery bars) decided to put this thing through the wringer, take a deep dive into the latest fitness tracking wearable and find out the answer. Enjoy, leave your questions, comments and feedback below, and if you decide to grab one of these bad boys for yourself, you can just go to the WHOOP website and use code “GREENFIELD” to save a whopping $50.
WHOOP Development and Background
The WHOOP strap basically focuses on two main aspects of your body: strain and recovery. Your strain level is updated throughout the day and is based upon your level of activity and workouts. Meanwhile, you can think of recovery as how prepared your body actually is for that strain.
So if you read nothing else in this review, this is the main point: strain and recovery are measured, and these let you make educated decisions about what you’re going to do the rest of the day for workouts, rest, etc. In other words, based on what the WHOOP tells you, you get to decide whether you’re going to take a yoga class and lay on the couch eating deep-fried Twinkies or you’re going to go out and do back-to-back Crossfit WOD’s or spend the day with your mother-in-law.
The WHOOP strap itself was developed by Will Ahmed, a Harvard University grad and D1 athlete, who had a single, focused goal: “to unlock human performance.” While playing in D1 athletics as the captain of the men’s varsity squash team, Will was astounded by how little he and his teammates knew about their bodies. As young men whose days were filled with training, studying, and any social activities they could manage, performance optimization through awareness of daily activities and sleep was really not a huge priority – especially because there wasn’t an easy and time-effective way to quantify this stuff.
So Will partnered with two other Harvard peers, met with cardiologists and physiologists, read some 500 medical papers, and over four years of development, he solved this problem. Since then, over the past year WHOOP has been tested and used by professional athletes and teams, and the information it provides to coaches actually is pretty innovative. Rather than treating the whole team as one and prescribing the same workout to each member, the WHOOP allows a coach to review each individual’s level of recovery and then personalize the workouts based upon this information.
In this review, I’m going to focus on the WHOOP Strap 2.0 that was made available to the public in late 2016 and geared toward the individual athlete.
How Does The WHOOP Work?
Strap on your engineering hat and white lab coat, because the first thing we’ll take a look at is how this thing is built.
The WHOOP band has five embedded sensors that constantly monitor and track heart rate, heart rate variability, ambient temperature, accelerometry and skin conductivity from your wrist. It is those five metrics that contribute to WHOOP’s analysis of your strain, recovery and sleep. This tiny piece of tech collects over 100MB of data per day and can store up to 3 days’ worth of data. And WHOOP claims to be one of the most accurate wrist-worn fitness trackers.
If you’ve been following me for a while, then you know that I totally geek out over heart rate variability (HRV) and personally measure mine every morning. I have numerous podcasts and articles discussing how you can measure it and what it can tell you. In a nutshell, HRV is the measurement of heart rate irregularity (yes, your heart beats at irregular intervals). A high HRV has been correlated to improved athletic performance and training adaptation and a low HRV indicates risk of overtraining and injury. In fact, a study done on NCAA athletes using WHOOP found a 60% reduction in reported injuries. If you ask me, that’s pretty significant. The WHOOP’s constant monitoring of HRV then informs its recovery and strain statistics. More on this later.
Your resting heart rate, average heart rate, maximum heart rate, and heart rate recovery after an activity are all used to feed into WHOOP’s Recovery, Strain, and Sleep algorithms.
There is also a built-in accelerometer. The 3-axis accelerometer is simply capturing your movement from your wrist. Ambient temperature combined with other data apparently helps to calculate your body’s second-to-second responses within the environment of your activity. And the skin conductivity feature ensures the strap is accurately measuring data. I don’t completely understand this, but I trust that WHOOP’s bespectacled scientists and engineers do.
It is the use of your measured data to predict your performance level that sets the WHOOP apart. As your WHOOP gets to know you, and as you become better at understanding your data, you can adjust your behavior, food, supplements, training choices, gear, etc. Let's now take a closer look at each of the tracking metrics WHOOP measures.
Let’s take a look at the individual tracking metrics WHOOP provides…beginning with their infamous “Strain” score. Your WHOOP strain is given in two ways: your overall Day Strain and a Strain Score for an individual workout or activity. Day Strain is the total accumulation of strain your body received over an entire day. Workout Strain Scores demonstrate your level of cardiovascular effort during a designated period of time.
Your Strain Score is displayed on a scale from 0 to 21 with 0-9.0 being light, 10-13.9 being moderate, 14-17.9 being strenuous, and 18-21 being all out. This same scale is used for your Day Strain. Strain can only be accumulated, never taken away, throughout an activity or the day.
The WHOOP system quantifies this all using what they call their “Strain metric”. This metric is based on your learned resting heart rate and max heart rate to calculate your resultant cardiovascular exertion. The more time spent in the higher end of your individual heart rate range, the more you contribute to a higher Strain. Because the Whoop is constantly monitoring your Strain (not just during a workout) it gives a more accurate indication of how your daily activities contribute to needed recovery.
For example, below is a WHOOP app screenshot from a day without an actual workout, in which Day Strain accumulated to 14.1, the low end of strenuous.
That’s even with a few hours missing due to a sauna session and shower, during which the WHOOP was removed. The WHOOP has only been tested up to 140 degrees F, so it is not advised to wear the thing while sweating it out in a hot sauna. Strap removal for the post-sauna shower was out of convenience. More on this later.
The WHOOP system doesn’t track steps because, as Will explained to Digital Trends, “Steps can be misleading as a measurement of performance. We wanted to create a wearable that could help a fitness enthusiast or an athlete measure their performance in the context of recovery.” Makes sense to me given that I often break up my day with movement outside of walking, such as push-ups and air squats.
The WHOOP automatically detects your activity, but you can add an activity or workout, even retroactively, so that you can go into the app and analyze all of your data. After you’ve completed an activity, you’re asked a few questions, shown below.
By answering these questions, you’re able to compare your perceived exertion to WHOOP’s measurement of Strain. If they don’t link up, then you can start to correlate other contributing factors, such as a particularly mentally or emotionally stressful day and its impact on your performance…or even a highly active day leading up to your workout that wasn’t shown in a morning’s HRV and recovery score.
Recovery is basically how well prepared the WHOOP thinks your body is for Strain. By taking three key metrics during your sleep each night, WHOOP calculates your recovery and gives you your recovery level in the morning. The three metrics are Heart Rate Variability (HRV), Resting Heart Rate (RHR), and Hours of Sleep.
Because you can and should wear WHOOP 24/7, it gives you an extremely accurate HRV measurement that is taken during your last period of Slow Wave Sleep each night. No more strapping on your heart rate monitor first thing in the morning!
As you wear the WHOOP, it gets to know your baseline and will calibrate to your own physiology. It considers itself calibrated to you, personally, after four recovery measurements. The first few days it will just give you a Recovery Score by comparing your data to typical recovery metrics based upon your age, gender, and fitness level.
WHOOP then calculates how recovered your body is during your Sleep each night and reports your Recovery when your sleep is complete each morning. There are three key metrics that make up your Recovery:
Heart Rate Variability (HRV), as I explained earlier, is a measurement of heart rate irregularity, or the variation of the time interval between successive heart beats. WHOOP captures all this during your last period of Slow Wave Sleep each night. HRV is an indicator of the health of your autonomic nervous system, and when HRV is high, it is a sign that your body is ready to adapt to changing environmental conditions. In other words, high HRV means you’re recovered and ready for a solid workout. HRV is one of the factors WHOOP uses to calculate your Recovery Score.
Resting Heart Rate (RHR) is a measure of your heart beat when you are at complete rest. This is also captured during your last period of Slow Wave Sleep. Lower Resting Heart Rates over time are good and indicate improved fitness and Recovery.
The Recovery algorithm then gives you personal training recommendations, like focusing on recovery, taking on moderate strain, or going after a hard workout. Here’s a snapshot from Ashley’s desktop app:
This allows you to better plan your training and day’s workout, rather than complying to a traditional, out-of-the-box training plan. If you’re due for a hard workout, but your recovery is low, you may want to switch around your workouts and allow your body to recover so that you can be physically primed and really peak at that hard workout.
As you know, your body recovers while you’re sleeping – and the more quality sleep you get, the better your recovery the next day, especially your central nervous system and brain recovery. WHOOP determines your Sleep Performance by measuring the total amount of sleep you got as a function of the sleep it determined you needed. It is reported on a 0-100% scale. This Sleep Performance is one factor used to determine your level of recovery for the next day.
WHOOP has discovered some interesting facts while aggregating this data. For example, they have shown that sleep deprivation significantly impairs all aspects of athletic and cognitive performance and both time spent asleep and time spent in REM sleep are positively correlated with performance. Their sleep statistics are broken down into four separate stages: Slow Wave Sleep, REM Sleep, Light Sleep, and Wake.
Slow Wave Sleep (SWS) is when your body repairs and regenerates tissues, builds bone and muscles, and strengthens the immune system. Obviously, this is very important for athletes. SWS tends to occur more, and in longer intervals, at the beginning of the night than at the end. It accounts for 25-30% of total sleep time over the course of the night.
REM Sleep is when dreaming and memory consolidation occur. As the night progresses, REM periods increase in length. Usually the first REM period will occur after about 90 minutes and lasts only 10 minutes. A normal amount of REM sleep is 60-100 minutes, or roughly 20% of the night.
Light Sleep is basically the transition stage between Slow Wave Sleep and REM and comprises about 50% of the total sleep time.
Wake comes in two forms, Sleep Latency and Sleep Disturbances. Latency is the time it takes you to fall asleep, generally 5-35 minutes. Sleep Disturbances are short periods of wakefulness during a sleep period. WHOOP claims that for athletes, anywhere from 3 to 7 disturbances per hour is normal, and you can expect more frequent disturbances as time in bed increases. Wake, not counting sleep latency, accounts for about 5% of the total time in bed.
Finally, a night’s sleep consists of about 3-5 Sleep Cycles. A full Sleep Cycle involves your body transitioning from Light Sleep, to Slow Wave Sleep, to REM Sleep. To really geek out on this sleep cycle stuff, check out my podcast interview with Dr. Nick Littlehales here.
The WHOOP desktop app allows you to see your entire Sleep Performance broken down into the different sleep stages.
The mobile version of the app even has a Sleep Coach tool that gives you a suggested amount of sleep for the night, your recommended time in bed based on historical sleep latency, a suggested time to get in bed if you input your wakeup time, and you can even indicate whether you’re hoping to peak, perform, or just get by the next day and WHOOP will adjust your sleep performance goal.
Over time, WHOOP learns your sleep patterns and claims to very accurately detect your sleep. Upon waking, you’re then asked a series of questions that you can use to see how various pre-bedtime behaviors affect your sleep.
The usefulness of such questions (including, apparently, whether or not you have been “getting it on”) has been demonstrated by WHOOP data indicating such phenomenon as the effects of alcohol consumption lasting up to four days when it comes to sleep (depending on the volume of alcohol consumed, of course). Sex, booze and tobacco tracking: yet another way self-quantification can help improve performance.
During part of this review, I had an extremely gnarly travel schedule that left me far out of my element (including an inability to even be able to charge wearables) and really couldn’t commit to wearing a fitness tracker the whole time and giving it the 24/7 testing it deserves, so I tasked my assistant, Ashley (mentioned at the beginning of this article), with sporting the WHOOP for a few days so we could really geek out on app functionality. Let’s take a look at some more of her data, shall we?
The WHOOP syncs with a mobile app (only iOS for now, but apparently an Android version is coming soon) and a desktop app. They’re actually pretty sleek apps.
The mobile app gives you access to your One Day Overview, Strain, Recovery, and Sleep pages, your Sleep Coach page, Strap Status page for current heart rate and WHOOP connection and battery life, and you can record an Activity (or workout) and retroactively add Activities.
The web app gives you more detailed information about your Sleep and Activity. You can view detailed heart rate during Activity and Sleep and look deeper into your Strain, Recovery, and Sleep trends over time.
When you open the app (this is the iOS version), you get a daily overview, complete with day strain, calories, activities, recovery, sleep, battery life, and the time through which data is available.
Here are a couple more screenshots:
Or maybe she’s just working her butt off as my personal assistant. I can’t really tell you without knowing exactly how this metric is calculated.
Edit** Since publishing this article, Ashley received an answer from WHOOP Support regarding how calories burned are calculated. Here it is:
“1) We first get an estimate of your Basal Metabolic Rate (BMR) using widely accepted formulas based on height, weight, and gender (note these are set in your profile information).
2) As your Heart Rate rises, we also add to the BMR estimate an additional increasing function of heart rate. That is, for heart rates above a certain threshold the formula becomes Calories Burned = BMR + function(Heart Rate). This function formula is proprietary and we have worked on matching academic literature on energy expenditure at different levels of effort.
If you feel that these estimates could use tweaking, please let us know. We are always hard at work improving all of our algorithms. One important thing to note is that if you take the WHOOP Strap off during the day, you receive 0 calories for that time period so the total calorie burn for that day will be low.”
Anyways, from here, you can swipe left to the next screen showing your Day Strain. You get a cute little rundown or explanation of your Strain, sometimes comparing you to other WHOOP users or telling you what kind of recovery you can expect.
Pretty neat, eh?
Next up, with another swipe, you can see your Recovery summary. WHOOP reports your recovery on a 0-100% scale that is grouped into three color categories: green being 66-100% meaning your body is ready to peak physically, yellow indicates scores between 33-66% with your body being prepared to train at a moderate level, and the red zone is for scores at 0-33% signaling that you’re pretty rundown and should focus on recovery activities. You’ll get an HRV reading, your lowest RHR, and sleep quantity.
My dear assistant Ashley was gracious enough to provide us with every zone. Screenshots below.
Within the mobile app, you can click on the question mark icon for a full explanation of the metrics used to analyze Strain, Recovery, and Sleep Performance (not that you’ll need to after churning through this article). Within the web app, you can view your stats from a specific activity, like this:
The web app also enables you to view your data over a specific time period. Here’s Ashley’s Strain over a two-week period.
The WHOOP indicates a light usage, and because Ashley isn’t training for anything in specific at the moment, she admits to not adding some workouts she did during this time period as an Activity in WHOOP because she was really more interested in her overall Strain, Recovery, and Sleep scores. The WHOOP still detects movement, heart rate, and all of the other stats in a day without the addition of an Activity, you just don’t get a detailed look at a workout’s stats if it’s not recorded as an Activity.
You saw a single day recovery snippet previously in the article, but you can also look at recovery trends over time…
..including HRV over time…
And here is an example of sleep trends over time:
WHOOP Strap Design and Wearability
The WHOOP sensor is attached to a stretchy, waterproof strap that is adjustable to any length. It weighs 0.64 ounces on its own and with the battery pack attached to the Strap, it weighs 1.16 ounces. It is to be worn about 1cm above the wrist bone and should be nice and snug.
Because WHOOP claims that “you are an athlete 24/7”, you should constantly wear the WHOOP. They make this easy with a battery pack that charges separately from the strap via a mini USB that is then slipped onto the sensor and strap so that you can charge it while you wear it. It is important to note that the battery pack is not waterproof.
The WHOOP is constantly collecting data and emitting Bluetooth signals. However you can turn off the Bluetooth sync from your phone (for instance, on a plane or while you’re sleeping) because it stores up to three days worth of data. According to Will, WHOOP will only send data via Bluetooth when synced to your phone and isn’t constantly searching for it when not synced. So no worries about irradiating your body with bluetooth 24-7.
Because of the strap’s design and how the elastic band just rests over one side of the sensor while connected to the other side, it can sometimes get caught on things and turn on itself. This wasn’t a huge issue during normal wear, but Ashley did report it getting twisted while sleeping a couple times.
Here it is on Ashley’s wrist:
Although the strap and sensor are waterproof, Ashley opted to take it off for showers due to the discomfort of a wet strap that lasted at least an hour. WHOOP explains that you can solve this problem by ordering more nylon straps (in various different colors), which are pretty cheap at $15.00 a pop.
WHOOP Battery Life
Because there’s no display on the WHOOP sensor, battery life can only be gauged from your wrist by tapping the band and seeing how many of three lights illuminate. Otherwise, you open the app to get a percentage of battery life.
WHOOP claims a 44 hour battery life with typical use. Because you charge the battery pack separately and then just slip it on the sensor while wearing the device, I never actually tested the battery life while wearing it. I would just put on the battery pack whenever I thought about it or when charge was around 20%. I didn’t have any issues with the battery life and never lost data due to a dead battery or being unable to charge it. You’ll also get an app notification when battery life falls below 10%.
Here’s the real kicker: compared to other wearables, this things costs a pretty penny, specifically to the tune of 500 dollars. Is it worth it?
I’d say that totally depends on your goals.
My assistant Ashley absolutely loves the thing.
As you might know, in the past I have sworn by (and still wear) my Oura ring. However, the way teams are using WHOOP to individualize training and performance is truly unique and useful and I can see the applicability for elite athletes or even serious recreational athletes.
I’m just not convinced your average fitness enthusiast will give a big enough WHOOP about their performance and recovery to shell out the money for this device. If you like to own nice things and you like to self-quantify, you’ll dig the WHOOP.
And if you’re a coach or a trainer trying to get the most out of your athletes or clients, and can oversee all their data at once because they’re all wearing WHOOP straps, then this is a no brainer (and yeah, you do save $50 with code GREENFIELD at WHOOP.com.)
WHOOP Summary & Final Thoughts
Overall, a strap that has obviously helped a large and growing number of professional athletes and teams to improve performance seems extremely useful to the individual and a big bonus for athletes, teams and coaches, assuming they’re serious enough or geeked-out enough about self-quantification to fork out the $500.
I think it’d be especially useful if, in the future, if WHOOP could integrate or sync with any of the nutrition apps out there to give a more quantified picture of how nutrition and hydration affect performance, recovery, and sleep. I think even being able to add when food is consumed and comparing how it made you feel physically to your WHOOP metrics could also be super insightful. Perhaps that’s because I love to eat, and I love to see how the food affects my body. Or perhaps I’m just ultra-picky about my self-quantification devices.
Of course, I can totally see (and hopefully you can too after reading this article) how Strain and Sleep metrics positively change user’s behavior, and Ashley strongly agrees (but needs to sleep more than 3:42 a night – sheesh girl). This has been evidenced by WHOOP data collected on NCAA athletes finding that they started sleeping an additional 41 minutes each night, reduced reported injuries by 60%, reduced self-reported illnesses by 53%, lowered resting heart rate 4.4 BPM, increased heart rate variability by 8 milliseconds, reduced alcohol use before bed by 79%, and reduced caffeine use by 86%. That’s pretty major, and you can view it all on their website here.
In summary, I give this strap a big whopping (or whooping?) thumbs up. If you want to try this bad boy out for yourself, just click here to go to WHOOP.com and use code GREENFIELD to save $50. Do you have questions, thoughts or feedback for the WHOOP team, for Ashley or for me? Leave your comments below and one of us will reply!