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Whoop 4.0 Wearble Sleep Tracker

Sleep Foundation Special Offer

Use this SleepFoundation.org link for the most current discount on WHOOP products

The wearable WHOOP tracker is a two-in-one device that uses both fitness and sleep data. The goal is to calculate overall recovery, which WHOOP defines as how prepared you are for activities in the day ahead based on your recent exercise, heart rate, and how well you slept the previous night.

The WHOOP has cultivated a major following within CrossFit and other workout communities. Many pro athletes also wear the tracker. That said, virtually anyone — even nonathletes — can benefit from the WHOOP’s comprehensive tracking system.

I recently had the pleasure of personally wearing and testing the WHOOP 3.0 for one week. Below you’ll find my breakdown of how the WHOOP operates, what it tracks, how it feels, and how well it works.

Due to shipping delays, I was unable to personally test the WHOOP 4.0, the latest version of the tracker that debuted in the fall of 2021. I’ve highlighted some of the key differences between the 3.0 and 4.0, but ultimately both iterations of the device are quite similar in terms of design, functionality, and operation.

What Does WHOOP Do?

The WHOOP is a wearable tracker with built-in photodiode sensors to monitor a wide range of metrics. The tracker is designed to be worn at all times. The more you wear it, the more accurate and consistent your personal data will be.

Metrics tracked by the WHOOP fall into three general categories: fitness, sleep, and recovery.

Fitness Tracking

The WHOOP calculates Strain Score, a proprietary scoring system that measures how physically active you’ve been. This score changes throughout the day based on what you do and how hard you push yourself.

Strain Score is calculated based on your heart rate after different activities in relation to your maximum heart rate. The WHOOP is specifically tailored to each wearer based on heart activity, fitness level, and performance ability. Your score could significantly differ from another person’s, even if you’ve both completed the same physical activity.

Strain Score is measured on a scale of 0 to 21. Here’s a breakdown of how to interpret these numbers:

  • Light (0 to 9): You have placed a low amount of stress on your body so far that day and are primed for more activity.
  • Moderate (10 to 13): You may have put some stress on your body, but there’s still room for activity before you call it a day.
  • High (14 to 17): You have placed a lot of stress on your body and have reached most of your daily fitness goals.
  • All Out (18 to 21): Your day has been exceptionally active, possibly to the point of affecting recovery for the following day.

The WHOOP also calculates Day Strain, a rundown of all your activities within a 24-hour period and the amount of collective stress placed on your body. This feature is particularly useful if you’re gearing up for a race, competition, or other event that requires days or weeks of preparation.

You can also access the Strain Coach function at any time. This feature issues alerts when you should push harder to reach your goals, when you’ve reached your goal, or if you should take a breather due to too much strain.

Sleep Tracking

The WHOOP is similar to other sleep trackers on the market in terms of the metrics it monitors. Each morning you’ll receive a detailed report of your sleep from the previous night. These reports cover the following:

  • Time in Bed, Hours of Sleep, and Sleep Efficiency: The Time in Bed metric refers to how many hours you physically spend in bed over the course of the night. This is weighed against the hours you spend sleeping to calculate your sleep efficiency score, which is measured on a 0% to 100% scale. For example, if you spend eight hours in bed and sleep for nearly eight hours, your sleep efficiency score will be higher than if you sleep for seven hours or fewer during the same amount of time in bed.
  • Sleep Stages: The WHOOP parses sleep into four different stages: awake, light sleep, rapid eye movement (REM), and slow-wave sleep (SWS) — or deep sleep. Healthy sleep is contingent on light exposure and time spent in REM and SWS stages each night. On the app, you can view a detailed breakdown of each stage for any given night.
  • Disturbances: This metric refers to the number of times you wake up during the night, whether consciously or not. Your body is almost completely at rest during deep sleep, so the WHOOP measures disturbances using position changes and other indicators that you have come out of deep sleep.
  • Respiratory Rate: This refers to the number of breaths you take per minute while sleeping.

The WHOOP also calculates Sleep Needed, which is based on your normal sleep patterns and your Day Strain score leading up to bedtime. Since you’ll need more rest after a day full of strenuous activity compared with a less active day, the amount of sleep you need fluctuates throughout the week.

The Sleep Needed metric also takes sleep debt into account. For example, if you needed eight hours of sleep last night and only slept for seven hours, then the hour of sleep debt you have accumulated will factor into the amount of sleep you need tonight.


Recovery pulls from a wide range of fitness and sleep tracking metrics. These include heart rate variability, or the amount of time between heartbeats during sleep. Another factor is resting heart rate, or the average number of heartbeats during the night. The latter is a weighted average, with heartbeats during SWS getting more weight because your heart rate slows during deep sleep. Other metrics used to calculate recovery include:

  • Respiratory rate
  • Hours of sleep
  • Fitness level
  • Strain scores
  • Overall health
  • Stress
  • Diet and hydration

Measured on a 0% to 100% scale, recovery scores are interpreted using three color-coded categories:

Color% RangeInterpretation
Green67% or higherYour body is ready for strain from physical activity.
Yellow34% to 66%While your body may be able to handle a high load of physical training, strain or poor sleep may hinder your efforts.
Red33% or lowerYour body may need a day off or a low training load until you have had adequate time to recover.

It’s important to take recovery seriously. If you haven’t properly recovered from your previous strain, you are at greater risk of injury. Excessive strain can also occur if your body isn’t prepared for the workout you have planned for that day.

The WHOOP issues weekly and monthly reports. You’ll automatically unlock the Weekly Performance Assessment tool after logging 14 recovery scores. For the Monthly Performance Assessment, you’ll need 28 recovery scores. These assessments include detailed breakdowns of strain, sleep, and recovery within that period. You can also see how you’ve performed versus other WHOOP wearers within your demographic.

WHOOP 3.0 vs. 4.0

As with any next-gen product, the WHOOP 4.0 has been modified with some additional functions that aren’t available with the 3.0. These include:

  • Tracking for pulse oximeter, blood oxygen, and skin temperature
  • More photodiodes used to track metrics
  • A built-in motor that issues vibrations when using the sleep coaching program

As I noted earlier, shipping delays prevented me from trying out the WHOOP 4.0 firsthand, so I can’t speak to this model’s modifications. However, their absence didn’t really affect my experience with the WHOOP 3.0, which was overwhelmingly positive. If you’ve used the 4.0, we’d love to hear your feedback on how well these new features perform and how much they’ve impacted your overall WHOOP experience.

How Does the WHOOP Look?

At first glance, the WHOOP looks fairly nondescript. The tracker does not have a screen or interface of any kind. Everything you need to view is accessed through the app.

During our interview with Emily Capodilupo, WHOOP’s senior vice president of data science and research, she explained that the tracker was designed with simplicity in mind.

“We really wanted wearables to just disappear on your body,” Capodilupo said. She added that a smaller, more straightforward design translates to a longer battery life.

You can catch our full exchange with Capodilupo in the video above.

Important aspects of the WHOOP’s look and feel include the following:

  • Size: The WHOOP weighs about half an ounce, so the feel is comparable to a light bracelet. With the battery pack attached, the weight increases to a little over an ounce.
  • Band and Hardware: While the material of the band varies slightly depending on the model chosen, both the ProKnit and SuperKnit designs include elastane, giving it a soft and stretchy feel. The clasp is composed of stainless steel, and the WHOOP 4.0 includes a component known as the Fast Link Slider, which allows you to slip the sensor on and off the band with greater ease.
  • Colors: A wide assortment of colors and designs are available for the WHOOP band, including some limited edition styles. You can also choose from different colors for the metal hardware.
  • Any-Wear: WHOOP recently unveiled the Any-Wear apparel collection, which includes boxer shorts, sports bras, compression tops, and other workout gear designed with pockets to secure the tracker while you exercise. Designed for use with the WHOOP 4.0, these garments might be an appealing alternative if the WHOOP intrigues you but you don’t like wearing wristband trackers.
  • Battery: When fully charged, the WHOOP has a battery life of up to five days, depending on your activity level. It comes with an attachable battery pack that’s used to recharge the device. The battery pack is fairly lightweight, so you can charge the tracker even while you’re working out. A USB port allows you to recharge the battery pack.
  • Cleaning and Care: Per the company’s instructions, you should hand-wash the band and sensor as needed — but avoid washing the metal clasp. When you shower, take off the band and sensor and wash with soap and water. You should also clean the sensor with soap or sanitizing wipes two to three times per week.

In terms of appearance, the biggest difference between the WHOOP 3.0 and WHOOP 4.0 is sizing. The latter is about 33% smaller than the previous model.

Buying the WHOOP

The WHOOP is a subscription-based tracker. Rather than making a one-time purchase, you select a subscription plan after choosing a band design. The tracker and band are included with each subscription. Existing customers can purchase new devices from WHOOP’s online store.

Here are the nuts and bolts for buying a WHOOP tracker:

Standard Subscription OptionsWHOOP offers three standard subscription options:

Monthly: $30 per month
Annual: $239
24 Months: $399

The tracker and a band of your choice come with each subscription. Costs of the subscription plans differ for non-U.S. customers.
WHOOP ProThe company now offers a fourth subscription option. For an additional $12 per month, WHOOP Pro subscribers receive a 20% discount on all WHOOP accessories, one free accessory every three months, and free shipping and returns on all orders.
ShippingIf you reside in the U.S., the tracker will be shipped at a flat rate of $8.99. Shipping costs for accessories may differ. WHOOP also ships to Puerto Rico, Guam, Canada, Australia, New Zealand, United Arab Emirates, and most of Europe. Delivery costs depend on the location.
ReturnsYou can cancel your WHOOP subscription within 30 days of receiving the tracker and receive a full refund minus shipping costs. The company may or may not require you to return the tracker in order to qualify for a refund.
WarrantyRegardless of which subscription you choose, the WHOOP is backed by a lifetime warranty. All accessories come with 90-day warranties.

Sleep Foundation Special Offer

Use this SleepFoundation.org link for the most current discount on WHOOP products

An Interview With Whoop

Still have questions?

Our product experts have extensive experience testing just about every sleep product on the market. Send an email to [email protected] or call us at (877) 672-8966 with your questions and we’ll help you find exactly what you’re looking for.

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