How Does The Whoop Fitness Tracker Work?

What do golfer Rory McIlroy, NFL quarterback Patrick Mahomes, NBA star Kevin Durant have in common?

They all use the Whoop Fitness Tracker system, and McIlroy, Mahomes, and Durant are so impressed that they have invested in the company. It has famously become the “wearable of choice” for golf’s PGA Tour.

Whoop Fitness Trackers have three sensors built into the device, which measure heart rate, oxygen levels, and skin temperature. The system uses continuous readings to create a three-pillared set of data relating to the user’s sleep, exercise strain, and post-exercise recovery profiles. The goal is to provide personalised recommendations and AI-assisted coaching feedback.

The Whoop Fitness Tracker provides an accurate and deep level of data to allow an athlete to make fine adjustments to their daily routine in the pursuit of optimised health and improved performance.

It’s not the only tool to offer fitness coaching, but the Whoop band’s biometric tracking is some of the most sophisticated of its kind.

How does it work? And is it worth the premium subscription?

How Does The Whoop Fitness Tracker Work? 

How does the Whoop Fitness Tracker work?

While other wearables offer a wide range of information data points, the Whoop Fitness Tracker is a dedicated system calibrated to athletic performance.

The device includes Five LEDs, four photodiodes, and a body temperature sensor.

Let’s take a look at each of the key sensors:

  1. Heart rate sensor
  2. ECG Sensor
  3. Electrodermal Sensor
  4. Sp02 sensor
  5. Bioimpedance sensor
  6. Temperature Sensor 
  7. Manual Data Input

Heart Rate Sensor

The whoop fitness tracker includes an optical heart rate sensor that continuously measures your pulse, or speed of blood flow. 

The Whoop Fitness Tracker differs from many other wearable devices in that it focuses on heart rate change and variability. The system can then report on how the heart is being strained during exercise or how it is recovering.

Other trackers do this too, but the sensors on the Whoop are considered ‘best in class’ as they collect the data more often.

ECG Sensor

This sensor provides the system with a reading of the tiny electrical impulses produced by the heart and can inform on the heart’s condition – post exercise and during.

Electrodermal Sensor

The electrodermal sensor measures stress along with the  Heart Rate Sensor, the ECG, and the heat Sensor.

The electrodermal sensor, with the other three sensors, can provide a report on the user’s overall stress levels by measuring tiny traces of sweat.

Other devices can provide a broad estimate of your current stress levels, but it’s the combination of these different sensors that gives the Whoop system such an advantage over the field.

SP02 Sensor

The SP02 sensor measures blood oxygen levels or oxygen saturation in the user’s blood.

The SP02 sensor uses two LEDs that emit light at different wavelengths — one red and one infrared. 

Fully oxygenated blood absorbs more infrared light, while blood with an oxygen deficiency does not, allowing more of it to pass through. By measuring the varying absorption of the light, the SP02 sensor calculates the percentage of oxygen in the user’s blood.

When the body is exerted, the person will start breathing heavily, which is responding to the need to improve the blood oxygen level.

Whoop sensors

Therefore, the system can interpret how the body manages exercise by reading the blood oxygen saturation percentage and how fast it changes. It’s like having an advanced VO2 Max tracker strapped to your wrist.

When the blood oxygen levels drop too low, the user may be overdoing it and possibly damaging the body. For athletes who are looking to train on the edge, this feedback is critical.

It can be the difference between maximised performance… and injury or burnout.

Bioimpedance Sensor

A bioimpedance sensor measures your skin’s resistance by measuring the ohms (Ω) of a tiny electrical current applied to the skin.

The system can measure sleep, heart rate, respiration rate, and water levels.

Skin Temperature Sensor

The skin temperature sensor measures very small fluctuations in skin temperature. Besides using the sensor to gauge exercise activity, it is also a predictor of illness and menstruation cycles.

The device is so sophisticated that you can predict illness hours or days before it arrives just by small changes in the temperature of the skin.

It’s useful for judging when is a good (or bad) time to step up the intensity of a training regime.

Manual Data Input on the Whoop

The Whoop system also gives the user an option to provide subjective data via several daily surveys, which include 

  1. The amount of alcohol consumed.
  2. Tobacco smoked.
  3. Screen use
  4. Medication (particularly new medicine).
  5. Shared bed.
  6. Reading traditional (non-screen) material.
  7. Caffeine use

The system correlates this data against the physiological data collected and determines the impact of each variable.

By taking advantage of the Whoop’s coaching system, you’ll get personalised recommendations that you can use to split test your daily behaviors.

“Should I have that cup of coffee before my race?”

With the manual inputs, life becomes an experiment.

While manual data input requires a certain degree of dedication (and honesty) on the part of the athlete, it’s a fantastic way of drawing correlation between lifestyle choices and baseline performance.

Professional athletes are called “professional” for a reason. It’s these extra steps that every great coach loves to see in his or her students.

What Is Different About the Whoop Fitness Tracker?

Whoop Fitness Tracker

The Whoop fitness tracker has approached the concept of being able to optimize fitness very differently from other devices.

The Whoop device features no screens, no GPS, and no pedometer.

If you want a multi-purpose wearable that can check your email as well as your pulse, there’d be no point in pursuing the Whoops. It can’t.

The result is that the Whoop Fitness Tracker doesn’t provide:

  1. Tracking of steps
  2. Tracking of stairs climbed
  3. Active minutes
  4. Notifications
  5. A screen to navigate
  6. A clock or watch-face
  7. A timer
  8. Any form of contactless payments!

The reason is that irrespective of your activity, the Whoop Fitness Tracker measures the impact on the wearer’s body and how quickly the body recovers from the activity.

That’s what it does, and anything else would be a distraction.

It’s solely dedicated to your physiological ‘vital signs’, and lacks the commercial crowd-pleasing features of a Garmin or Apple Watch.

The device is tiny and can be worn on the user’s wrist or on a comfortable bicep band, and the user soon stops noticing it.

It is waterproof up to 10 meters for 2 hours and can be worn 24 hours a day, even in the shower, swimming pool, or during shallow scuba dives.

The device can be recharged while worn by attaching the recharging battery.

At its heart, the system is designed to monitor three main “columns” of body performance which include:

  1. Sleep
  2. Exercise strain
  3. Recovery from exercise

Track Sleep

The sleep functionality analyses sleep quality and reports the different sleep patterns.

  1. Time In Bed Awake
  2. Light Sleep
  3. Rem Sleep
  4. Deep Sleep (Slow Wave Sleep)
  5. Disturbances
Sleep analysis using Whoop

It also reports on how much time was spent in bed against how much time was needed for sleep.

The Whoop excels here. It tracks sleep more accurately than any smart watch or step counter we’ve tried – mainly because it has the unrivalled sensors to do so.

Track Recovery After Exercise

By monitoring recovery, the user can see how the body adapts to factors like stress, work, nutrition, training, etc.

Some of the following measures are available on other fitness wearables, but the Whoop boasts lab-based evidence that it does a better job.

Heart Rate Variability

This system measures very small changes between each heartbeat, which can be used as an indicator of how the body is coping with training. It can also be used to predict future illness.

Resting Heart Rate 

The system compares the heart rate every night to establish a baseline resting heart rate. If you deviate from this, it can be indicative of a stressed body.

Respiratory Rate

Again, if this deviates from the baseline, it may indicate a problem.

From the three measurements, the Whoop system generates a traffic light system of readiness for the next exercise session.

  1. Green  – ready for exercise.
  2. Yellow – body needs some rest.
  3. Red – take more time for rest and active recovery.

This is one of the areas where many athletes run in to confrontation with their fitness tracker of choice – and the Whoop is no different.

If you’re raring to train but your coaching app says that you’re in dire need of recovery – how are you going to resists the urge to workout?

Many people can’t.

From our experience, while the Whoop does a much better job than similar tools (like Garmin’s recovery tracker), it doesn’t always match up to a subjective assessment of true exhaustion.

Track Strain During Exercise

Activity strain

As you begin strenuous exercise, the system provides three ranges of measurement:

Light Strain (0-9)

The body is coping well.

Moderate Strain (10-13)

This range indicates moderate stress is being put on the body, which helps maintain fitness.

High Strain (14-17)

This indicates increased stress or activity, which can help build fitness gains in the user’s training – but should be used sparingly to avoid burnout.

Overreaching (18-21)

Training has put significant stress on the body, and recovery will take longer.

AKA you’ve pushed it too far.

Pros of The Whoop Fitness Tracker

What are some of the key positives of the Whoop system?

It’s Very Simple To Use

This system comes impressively packaged in a simple band that is attached and forgotten about. It is waterproof, light, and easy to forget on your wrist. It recharges by using a battery that slides over the strap while still on your wrist and works seamlessly.

If the goal is to get out of the athlete’s way and crunch data in the background, it has to be said that the Whoop is very well designed.

Lots and Lots Of Data

The main benefit of the Whoop Fitness Tracker is the mobile app and how it provides insights, including a weekly and monthly performance assessment.

Unlike basic smart watches and fitness bands, the sensors on the Whoop provide a highly accurate breakdown of your physiological readings – and this is relayed in to an app that is beautifully designed and simple to view.

Useful Haptic Alarms

The system can allow you to set alarms based on your daily performance goals. The device vibrates for 30 seconds when the next session is due.

There aren’t many bells and whistles compared to, say, an Apple Watch – but the smart alarms (like waking you up at the optimal moment of a sleep cycle) are well thought out.

Understated Design

Users can wear the tracker in many ways; even when worn on the wrist, it’s barely noticeable.

Cons of The Whoop Fitness Tracker

So what are the drawbacks?

Expensive Monthly Subscription

Whoop requires a monthly subscription fee of $30, or an annual payment of $288 for two years of ownership. 

This is at the premium end of the market.

It might be loose change if you’re one of the PGA Tour golfers sporting the device, but it’s expensive for the average consumer.

No Screen

There is no screen which means that for information like time, calendars and timers, you still need to wear a watch, which is cumbersome. The device doesn’t track much beyond recovery and has no display, no clock, or pedometer.

Battery Life Is Inadequate

The battery only lasts 3 to 3.5 days which is less than the 5 days predicted by Whoop.

A Word of Caution About Fitness Trackers

The newest trend of analysing a play-by-play assessment of our bodies during a routine might provide interesting information for trainers or coaches.

However, we aren’t robots; we all have good and bad days, including drinking alcohol, spending time with family, and being stressed about the next day’s game.

These fitness tracking devices do not consider context, and sometimes the true story of what’s happening is hidden in the context. You might know why you’re feeling particularly stressed on a given day, and it may have nothing to do with how you slept or how you worked out yesterday.

At the time of writing, 50 teams and 12 schools within the National Collegiate Athletic Association (NCAA) have adopted the WHOOP band.

Striking the right balance between tracking physiological changes and empowering an athlete to live a balanced lifestyle is not going to be easy.

The data from Whoop (and similar systems) is useful, of course.

But the technology is still developing and should be used in conjunction with common sense. Every athlete should have an understanding of his/her body that goes beyond the instructions of a personalised coaching assistant.

Our View on the Whoop Fitness Tracker

The Whoop Fitness Tracker is a valuable tool in your daily fitness routine, but only if you are willing to place faith in what some still deem to be ambiguous readings.

There’s no doubt, the device does provide an excellent level of data analysis – and its sensors are meticulously designed for extracting physiological insights.

In our view, the Whoop Fitness Tracker is probably not worth a $30 per month subscription to the average amateur data cruncher.

But for professionals and those seeking marginal gains in every possible aspect of their fitness, this device will give you a LOT of food for thought.

Author Profile

Alex Randall

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Alex is the editor at Revel Sports. It was his idea to take our post-club-run chats and build a website out of them. He is responsible for dotting the I’s and crossing the T’s when any of us have something to post. (Basically: it’s all his fault). A ferocious 5K powerhouse on his day, Alex is known for not understanding the meaning of the term ‘negative split‘.
Alex Randall

Revel SPorts Contributor

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