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Polar Loop with Keely, or Apple Watch.
An Apple Watch is a screen on your wrist with GPS and a battery of up to a day; a Polar Loop is a screen-free band that lasts days. Apple’s own Readiness score, new in September 2026, needs a Series 12 or an Ultra 4, from $399. Apps such as Athlytic and Bevel turn any Apple Watch’s data into recovery scores. A Polar Loop is $199.99 once, and Keely is free. They also work together: Keely can read the walks and runs your Apple Watch saves to Apple Health for its VO2 max.
Updated
At a glance
| Polar Loop with Keely | Apple Watch | |
|---|---|---|
| Price (US) | $199.99 for the Loop, once. Keely is free | SE 3 from $249, Series 12 from $399, Ultra 4 from $799 |
| Subscription | None | None for its health features |
| Screen and GPS | Neither: a band | Both |
| Battery, by the maker | Up to 8 days (Polar’s figure, with Polar Flow) | SE 3 up to 18 hours; Series 12 up to 24 hours |
| Morning score | Recovery, 0–100 %: HRV, resting heart rate, sleep, breathing rate and skin temperature | Readiness, 0–10, from Recover to Go for it, on Series 12 and Ultra 4: from your activity, Training Load, vitals and sleep score |
| Effort | Load: points per minute by heart-rate zone, no ceiling, with a target range each morning | Training Load: your last 7 days of workouts against the 28 before |
| Sleep | Stages from the Loop, need (goal, debt and a hard day), consistency and a lights-out time | Sleep Score, 0–100: duration, bedtime consistency and interruptions |
| VO2 max | From your walks and runs: their pace in Apple Health against the Loop’s heart rate, with a likely range | Cardio Fitness, from outdoor walks, runs and hikes on Series 3 or later, in four levels for your age and sex |
| An age | Keely Age, from your VO2 max alone, each Monday | Health Age, announced for the redesigned Health app “later this year”, using measures such as VO2 max, resting heart rate, sleep and HRV |
| Phones | iPhone | iPhone |
| Your data | Raw heart data stays on your iPhone; your account backs up daily summaries | In Apple Health, with an export of everything as XML |
Facts about Apple Watch come from Apple’s own pages, checked October 5, 2026. This page compares cost, scores and data; it doesn’t test sensor accuracy.
With Athlytic or Bevel
These iPhone apps read your Apple Watch’s data from Apple Health and turn it into recovery, effort and sleep scores. They need a watch on your wrist; Keely needs a Polar Loop.
| Athlytic | Bevel | |
|---|---|---|
| Price (US) | $29.99 a year or $4.99 a month, after a 7-day trial | Free; Pro is $14.99 a month or $99.99 a year |
| Scores | Recovery (0–100 %), Exertion (0–10) with a target, Sleep, Battery and Stress | Recovery, Sleep, Strain, Stress (0–100) and Energy Bank, all free |
| VO2 max | Used in Athlytic Age; Athlytic reads its data from Apple Health | Read from Apple Health: Bevel doesn’t calculate its own |
| An age | Athlytic Age: resting heart rate, VO2 max, sleep, body composition, steps, training minutes and heart-rate recovery | Biological Age, with Pro: sleep, activity, resting heart rate and more, with blood biomarkers |
| Works with | Apple Watch, and other wearables that save HRV to Apple Health | Apple Watch, Garmin, Oura, and Google Health or Fitbit |
| Your data | Read and processed on your iPhone | Your Apple Health data stays on your iPhone unless you turn on Bevel Intelligence |
Using both
If you already run or walk with an Apple Watch, Keely can read the outdoor walks and runs it saves to Apple Health, with their distance, and pair their pace with your Loop’s heart rate for its Fitness estimate. Keely also saves its sleep, workouts, resting heart rate and breathing rate to Apple Health.
Where Apple Watch does more
- A screen, GPS and haptics. Workouts, pace and alarms on your wrist, and a VO2 max measured during outdoor walks, runs and hikes, with nothing else to carry.
- Readiness through the day. On Series 12 and Ultra 4, Readiness updates as new data comes in.
- More sensing. An ECG on Series 4 and later (not SE), blood oxygen (not on SE 3), and sleep apnea notifications on Series 9 and later and SE 3.
- Low cardio fitness notifications, with a white paper on how Apple validated its VO2 max estimate.
- Coming: Health Age and an at-home VO2 max test, announced September 9, 2026.
- Your data, out. Everything in Health exports as XML. Keely doesn’t export yet.
Where Keely is different
- Days on a charge, nothing to look at. The Loop lasts up to 8 days by Polar’s figure, so it can stay on through every night.
- A Recovery score without a new watch. Keely scores every morning on any iPhone that runs it, with each input shown. See Recovery.
- Stress as a number, live. From 0 to 100 while Keely is open, and never scored while you move. See Stress.
- A Load target each morning, from your Recovery and your last four weeks. See Load.
- Keely Age, today, with its formula. From your VO2 max alone, turned into years through the evidence on fitness and mortality. See Keely Age.
- Every formula is public, on the methodology page.
- Your raw heart data stays on your iPhone.
Frequently asked questions
Do I need an Apple Watch for Keely?
No. Keely works with a Polar Loop and an iPhone. For its VO2 max, it needs walks or runs with their distance in Apple Health, which an Apple Watch, another watch, or an app such as Strava can save.
Does Apple Watch have a recovery score?
Since September 2026, Readiness, from 0 to 10, on Apple Watch Series 12 and Ultra 4. Other models, SE 3 included, don’t get it. Apps such as Athlytic and Bevel give any Apple Watch a recovery score from its data.
Is Keely Age like Athlytic Age or Bevel’s Biological Age?
They’re built differently. Athlytic Age and Bevel’s Biological Age combine several measures, from sleep to steps. Keely Age comes from your VO2 max alone, against the evidence on fitness and mortality, and its formula is published.
Is Keely’s VO2 max like Apple’s Cardio Fitness?
Both come from walking and running outdoors, and both place you among people your age and sex. Apple Watch measures your pace itself; Keely takes the pace from Apple Health and the heart rate from your Loop. See Fitness.
Sources
- Prices: Apple Watch SE 3 and Introducing Apple Watch Series 12 (September 9, 2026). Apple Fitness+: apple.com.
- Readiness: Apple Support (September 14, 2026). Vitals: Apple Support (September 14, 2026).
- Training Load and Sleep Score: Apple Watch User Guide.
- Cardio Fitness: Apple Support (September 14, 2026), Cardio Fitness notifications (December 14, 2020) and Apple’s white paper (May 2021).
- Health Age and the VO2 max test: Apple advances health and fitness capabilities (September 9, 2026).
- SE 3: specifications. Export: Share your health data.
- Athlytic: athlyticapp.com and the App Store.
- Bevel: Free and Pro, scores and devices (each September 30, 2026), Biological Age (July 8, 2026) and privacy policy (September 30, 2026).
- Polar Loop price: Polar’s US store. Specifications: Polar Loop user manual.
All checked October 5, 2026. Prices and features change, so check theirs before you buy. Apple, Apple Watch and Apple Health are trademarks of Apple Inc.; Athlytic and Bevel are trademarks of their owners. Keely isn’t affiliated with or endorsed by Apple, Athlytic, Bevel or Polar.
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