Whoop
Whoop · Strain & Recovery Band
Evidence grade 3 of 5, Mixed. Read how the Atlas grades evidence.
0 human trials, about 14 studies, Validation cohorts mostly small (single-digit to ~30 subjects); a 2025 nocturnal study used 13 adults across 536 nights. The written rationale for this grade is still being prepared.
- FDA
- WHOOP MG ECG software got FDA 510(k) clearance (K243236, April 2025) for AFib detection; a July 2025 FDA warning letter says the Blood Pressure Insights feature lacks clearance. Core strain and recovery scores are unregulated wellness features.
- WADA
- Not a prohibited device; legal in competition. WHOOP holds many pro-sport partnerships (PGA Tour, F1) but data is not used for anti-doping.
Reference only. Not medical advice.
What can go wrong
Wrist photoplethysmography loses accuracy during motion and can perform worse on darker skin tones or with a poor fit, and sleep staging is only moderately accurate. The Recovery and Strain scores are unvalidated proprietary estimates rather than clinical readings and should not guide diagnosis or medication decisions. Daily scoring can also fuel over-reliance and anxiety, a pattern sleep clinicians call orthosomnia, where chasing a good sleep score actually worsens sleep. Anyone using the device to manage a heart, sleep or blood-pressure condition, or noticing persistent off-baseline readings, should confirm findings with a qualified clinician rather than act on the app alone. People prone to health anxiety or disordered patterns around exercise and rest may want to discuss wearable use with a provider before relying on daily scores.
WHOOP is a screenless subscription wrist band that uses photoplethysmography to capture heart rate, heart rate variability, respiratory rate and skin temperature, then folds them into proprietary Recovery, Strain and Sleep scores. The raw signals have reasonable independent support. Bellenger and colleagues (Sensors, 2021) found acceptable heart rate agreement against ECG and low HRV bias with WHOOP's own filter, and Dial and colleagues (Physiological Reports, 2025) measured moderate accuracy for nocturnal resting heart rate and HRV across 536 nights, though it trailed the Oura ring on both. Sleep is a mixed story: Miller and colleagues (Journal of Sports Sciences, 2020) validated wake-versus-sleep at 89 percent agreement against polysomnography but found four-stage staging weaker at 64 percent. The honest gap sits in the scores themselves. Recovery and Strain are black-box composites whose weighting is undisclosed, and Lundstrom and colleagues (2023) found they did not correlate with objective stress markers in trained athletes, so they are estimates rather than measured quantities. WHOOP's own high accuracy figures should be read as the company's claims. On the regulatory side, WHOOP earned a 510(k) clearance for ECG-based atrial fibrillation detection in April 2025, then drew an FDA warning letter in July 2025 over an unauthorized Blood Pressure Insights feature; that letter was closed out in June 2026 after WHOOP changed the feature.
Membership-only wrist band that turns nightly HRV and heart rate into proprietary recovery, strain and sleep scores
What people take it for
These are the reasons people give for taking it. They are not effects it has been shown to have.
What people get wrong
Often saidWHOOP measures my recovery and stress directly.
ActuallyRecovery and Strain are proprietary composites of HRV, heart rate and sleep with undisclosed weighting. Lundstrom et al. (2023) found the scores did not correlate with metabolic or psychological stress markers in trained athletes, so they are estimates, not measured quantities.
Often saidIts sleep stages are as accurate as a lab.
ActuallyAgainst polysomnography, Miller et al. (2020) found four-stage agreement of 64 percent with a kappa of 0.47. Wake-versus-sleep detection is solid at 89 percent, but fine staging is only moderate.
Often saidThe blood pressure feature was FDA-approved.
ActuallyThe FDA's July 14, 2025 warning letter stated Blood Pressure Insights had no clearance. Only the separate WHOOP ECG software holds a 510(k) clearance (K243236, cleared April 2025). The FDA closed the warning letter in June 2026 only after WHOOP modified the feature and its labeling, not by granting device authorization.
Often saidWHOOP is more accurate than other wearables.
ActuallyDial et al. (2025) ranked WHOOP 4.0 behind both Oura generations for nocturnal resting heart rate (concordance 0.91 vs 0.97 to 0.98) and HRV (0.94 vs 0.97 to 0.99) across 536 nights.
Who profits, and who pushes back
Dean J. Miller
For a wearable, distinguishing sleep from wake is reasonable, but classifying detailed sleep stages agrees with laboratory polysomnography only modestly.
Kelly Glazer Baron
Patients can develop a perfectionistic preoccupation with optimizing tracker sleep data, and that anxiety itself can worsen sleep rather than improve it.
Lundstrom et al.
The Strain and Recovery scores come from black-box proprietary algorithms and did not track objective metabolic or stress measures, so they are best read as educated estimates.
WHOOP Inc.
Sells this. Has a commercial interest in a product sold as this compound, as of July 2026.
Markets in-house validation and accuracy percentages.
Cristiano Ronaldo
Sells this. Has a commercial interest in a product sold as this compound, as of July 2026.
Equity stake plus paid endorsement.
PGA Tour
Sells this. Has a commercial interest in a product sold as this compound, as of July 2026.
Commercial sponsorship deal.
Rory McIlroy
Sells this. Has a commercial interest in a product sold as this compound, as of July 2026.
Financial stake in the company.
Where the research comes from
Most of the published research on this comes from one place. 62% of it is from North America. Findings that no unrelated group has reproduced are weaker than the study count makes them look.
| Place | Share of published research |
|---|---|
| North America | 62% |
| Europe | 20% |
| Asia-Pacific | 13% |
| Rest of world | 5% |
Research published from: USA.
How we got here
WHOOP grew out of Will Ahmed's frustration as Harvard squash captain trying to monitor his own overtraining. He founded the company in 2012 at the Harvard Innovation Labs with John Capodilupo and Aurelian Nicolae, and it seeded straps with NBA and NFL athletes before any consumer launch. It popularized the screenless, membership-only model, charging a recurring subscription rather than selling hardware, and iterated through WHOOP 4.0 and the 2025 WHOOP 5.0 and MG. The device sits in a long autonomic-monitoring tradition that reaches well beyond Silicon Valley. Photoplethysmography, the optical pulse sensing at its core, was first described in the 1930s. Heart rate variability entered cardiology in the 1960s, and much of the foundational HRV research through the following decades came from Russian and European physiologists studying cosmonauts and cardiac patients, formalized by a joint European and North American task force in 1996. WHOOP applied that older science to a wrist-worn consumer product and rode athlete endorsements to a multibillion-dollar valuation by 2026.
- 1930sPhotoplethysmography, the optical pulse sensing WHOOP relies on, is described in the research literature
- 1960sHeart rate variability is studied as a marker of autonomic and cardiac state, much of the early work in European and Soviet physiology
- 1996A joint European and North American task force formalizes HRV measurement standards, enabling later wearables
- 2012WHOOP is founded at the Harvard Innovation Labs by Will Ahmed, John Capodilupo and Aurelian Nicolae
- 2015The first WHOOP strap reaches early athlete and team users
- 2020Miller et al. publish the polysomnography validation in the Journal of Sports Sciences
- 2021WHOOP 4.0 launches and Bellenger et al. validate heart rate and HRV against ECG in Sensors
- 2023Lundstrom et al. report that Strain and Recovery scores do not correlate with objective stress markers in trained swimmers
- 2025WHOOP 5.0 and MG launch on May 8; the ECG feature gains FDA 510(k) clearance in April, and a July 14 FDA warning letter targets the Blood Pressure Insights feature
- 2026WHOOP raises a $575M Series G at a $10.1B valuation in March; the FDA closes out the blood-pressure warning letter on June 17 after WHOOP modifies the feature
At a glance
- Business model
- No hardware sale; membership only, roughly $199 to $359 per year (2025)
- Core sensor
- Wrist PPG plus skin temp and accelerometer; no screen, app-driven
- Headline metrics
- Recovery percent, day Strain (0 to 21 scale) and Sleep performance
- 2025 valuation
- About $10.1B after a $575M Series G, March 2025
What this entry does not yet cover
What follows is unfinished work on our side, not a finding about Whoop. A short entry is not a safe entry.
- Cost and market. We have not documented what it sells for or who sells it.
- Supply chain. We have not mapped where it is made.
- Who uses it. We have not documented the user groups.
- What could change. No forward-looking summary yet.
- How it compares. We have not set it against the alternatives.
- Children and teenagers. We have not checked what is known about younger people.
Sources
WHOOP validated against polysomnography: 89% wake-vs-sleep agreement (kappa 0.49), 64% four-stage agreement (kappa 0.47)
WHOOP heart rate agreement with ECG within 0.4% bias; low HRV bias with proprietary filter
WHOOP 4.0 nocturnal resting HR concordance 0.91 (MAPE 3.0%) and HRV 0.94 (MAPE 8.2%) across 536 nights, trailing both Oura generations
Strain and Recovery scores showed no meaningful correlation with metabolic or psychological stress markers in trained swimmers; scores derived from black-box algorithms
FDA warning letter states Blood Pressure Insights is an unauthorized medical device marketed without clearance
FDA Warning Letter, WHOOP, Inc. (MARCS-CMS 709755, July 14, 2025)
FDA closed the warning letter on June 17, 2026 after WHOOP modified the feature and labeling, citing updated General Wellness guidance; no device authorization granted for blood pressure
MedTech Dive, FDA drops Whoop warning letter over blood pressure feature
WHOOP ECG Feature 510(k) clearance (K243236, cleared April 4, 2025); 96.2% AFib sensitivity, 99.4% sinus-rhythm specificity, informational use only
Orthosomnia defined as a perfectionistic preoccupation with tracker sleep data that can worsen sleep
WHOOP raised $575M Series G at a $10.1B valuation on March 31, 2026; 2.5M+ members, $1.1B bookings run rate up 103% YoY
WHOOP 5.0 and MG launched May 8, 2025 with membership tiers at $199, $239 and $359; MG adds FDA-cleared ECG and blood-pressure estimates
WHOOP press release / Businesswire, WHOOP Unveils WHOOP 5.0 and WHOOP MG
Rowe v. Whoop class action citing the FDA warning letter, filed Nov 18, 2025, N.D. Cal., at an early stage with unproven allegations
ArentFox Schiff, Whoop There It Is: FDA Warning Letter Now Anchors a Class Action Against Whoop