User Guide

TL;DR

• Free tells you where you stand today; Sentinel tells you where you're heading. The Healthspan Index, Recovery Score, Strain and your VO₂ Max number are free.
• Everything is measured against you — your own 30-day baseline, not a population average. On Kreev's scale, 50 means your usual.
• Day 1 is already calibrated. Kreev imports your last 30 days from Apple Health when you install, so if you've been wearing your Apple Watch your baselines and today's scores exist on the first morning.
• You'll need an iPhone on iOS 16+ and an Apple Watch Series 4+ (watchOS 9+). Everything runs on your iPhone — no account, no server.

Look for a Sentinel tag next to any feature below that's part of the paid tier. The full comparison is at the end of this guide.

Day 1: already calibrated

1. Install and allow Apple Health.
2. Kreev imports your last 30 days. If you've been wearing your Apple Watch, your baselines and today's scores exist on the first morning — there is no two-week calibration period.
3. See your numbers. Your Healthspan Index, Recovery Score, Strain and VO₂ Max are free. The daily narrative appears on Day 1 if you start the Sentinel trial; otherwise you'll see the free readings.

Some things still need a runway of data — that's the first weeks table below. If you have no watch history yet, Kreev starts learning from the day you begin.

Your daily flow

1. Open the app in the morning — Kreev's 7 AM notification reminds you. If your Apple Watch sleep data is still syncing, you'll see a "Sleep syncing" chip and the score will refine itself once it arrives.
2. Read the narrative (Sentinel) — the paragraph on the Today tab is the morning briefing. It already accounts for last night's sleep, recent HRV trends, and yesterday's strain. On Sunday, a separate Weekly Debrief card appears below it — it adds a week-in-review on top of the daily narrative.
3. Tap the "How do you feel today?" check-in — five icons from exhausted to energized. One tap a day, free. It shapes the narrative's congruence line (Sentinel) and, after 60 days, one of your patterns.

That's the daily loop. Everything else is for the long game. The numbers below match the screenshots; on a phone they are simply the list under each image.

① Healthspan Index. A hero card leading the tab: your five components — VO2 Max, HRV, Resting Heart Rate, Sleep, and Sleep Regularity — each scored out of 20 on a segmented ring, for one number out of 100 and a tier label (Exceptional / Solid Foundation / Building Phase / Needs Attention). Free, with the full component breakdown. The six-month trend is Sentinel.

② Recovery score. The big number and surrounding arc are Kreev's morning verdict — 50 means your usual. Tap it for the full breakdown of HRV, sleep, RHR, and respiratory rate contributions, including an Analysis tab with your Top Contributing Factors — the two metrics most responsible for today's score, shown as personal-baseline deviations. Sentinel for the Analysis tab detail.

③ Strain. Your strain score. It increases during the day as you move. Tap it to open its own drill-down and see your strain distribution during the week, one month and six months.

④ Recovery vs Strain. Sits directly under Recovery and Strain — a 180-day chart of recovery vs strain so you can see whether your training load is in balance. Sentinel.

⑤ Narrative paragraph. Kreev's plain-English interpretation, written by its own rules on your iPhone, of today's signals — sleep, HRV, strain, and how today compares to your recent norm. Sentinel.

Daily check-in (not in this screenshot). The "How do you feel today?" card sits between Recovery vs Strain and the narrative — five icons, one tap. Free to tap; what it adds is described above.

⑥ VO₂ Max. Your estimate and, below it, where it ranks against ACSM norms for your age and sex. The number is free; the ranking and the distance to the next band are Sentinel.

⑦ This Week card. Reads your last four weeks and suggests the week ahead: which days you've historically recovered best on, how many hard sessions your current acute-to-chronic load ratio can absorb (0 to 4), and where the easy days have to fall — hard days always have at least one easier day between them. Each day is marked Intensity Window, Moderate, or Recovery; it suggests, never prescribes a workout, duration, or number. Needs 28 days of strain history to appear. Sentinel.

⑧ Today's Metrics. Your four overnight readings — HRV, sleep duration, resting heart rate and respiratory rate — each with how far it sits from your own baseline. They use Kreev's sleep-window aggregation, so they can differ slightly from Apple Health's daily figures. Tap any row for its trend: free shows the current week, Sentinel up to six months.

⑨ Activity. Your steps so far today, updating as you move. Tap for its own drill-down.

First weeks — what fills in when

Some of Kreev's surfaces need a runway of data before they say anything. Kreev would rather wait than guess.

If a card says "calibrating" or stays empty, that's by design.

The long game (Day 30 and beyond)

The daily briefing is the daily value. These are the strategic surfaces — each marked with its tier:

• Six-month Healthspan trend — Sentinel. See whether your five ageing markers are moving together or apart.
• VO₂ Max trajectory and ACSM rank — the number is free; the trajectory against age-and-sex bands and the rank are Sentinel.
• Boiling Frog detector — Sentinel. Catches the slow drift no single day shows.
• Autonomic Archive and Your Patterns — Sentinel. A heatmap per month for six months, and the patterns Kreev has found in your own data. A heatmap is a colour map: each day is coloured by its Recovery Score, so runs of amber or red show accumulated load, and a weekday that is always low shows up as a column. A pattern is an association in your measured data ("tends to," "goes with") — never proof of cause, and Kreev doesn't know your habits such as alcohol, caffeine or stress.
• Weekly Debrief and Month in Review — Sentinel. The narrative, zoomed out.

What Kreev does

Every morning at 7 AM, Kreev pulls last night's sleep, your HRV, resting heart rate, respiratory rate, and yesterday's training, and gives you a plain-English answer to:

"How recovered am I today, and what should I do with that information?"

That's the whole product. One short briefing, daily. Not another dashboard.

Kreev vs Apple Health

Apple Health stores your numbers. Kreev tells you what they mean today.

Use them together. Apple Health is the truth source; Kreev is the interpreter.

The "you vs you" idea

Kreev compares each morning's readings against your own 30-day average, not a population number. Reason: for HRV especially, two healthy people can sit at completely different "normal" values. A resting HRV of 35 ms might be alarming for one person and routine for another.

So when Kreev says "your HRV is below baseline," it means: lower than YOUR usual. The goal isn't chasing a perfect score — it's stability week-to-week and gradual improvement over months.

How to read the number: 50 means you're at your normal — not half recovered. Kreev's scale is centered on your own baseline, so an ordinary morning sits near 50 and it is built not to flatter you. A 45 and a 55 are both "around normal" for you; it's sustained drift below baseline, not a single day's number, that's worth paying attention to.

Plain-English glossary

A few terms in the drill-down screens come from sports science. Translated:

• Baseline — your 30-day average for that metric.
• Z-score — how unusual today is for you. 0 = totally normal. +1 = a good day. −1 = a recovery day.
• Standard deviation — how much your readings normally bounce around. Small = steady; large = variable.
• Strain — how hard yesterday's training was, based on your actual heart rate (TRIMP method). Not the same as Apple's exercise minutes.
• Recovery score — Kreev's morning verdict, combining HRV (35%), sleep (30%), resting heart rate (20%), and respiratory rate (15%).

"Is my baseline even any good?"

Fair question, worth a straight answer.

• VO2 Max has well-established population data normalized by age and sex (the ACSM categories). It's the one metric where Kreev tells you outright where you stack up — Poor / Fair / Good / Excellent / Superior.
• For HRV, RHR, sleep duration, respiratory rate, population norms are either weak or so broad they aren't useful. So Kreev's standard is your own trajectory. The rule of thumb:
  • If a metric is above baseline and you feel good → stable, healthy pattern. Green light.
  • If your baseline itself is moving in the right direction over weeks (Trends tab → Long-Term Direction card, Sentinel), that's the real win. Your baseline isn't fixed — improving it is the goal.
  • Worth raising with a doctor (independent of Kreev) if you consistently see resting heart rate above 80, sleep below 6 hours, or respiratory rate above 16 at rest. Those cross clinical thresholds where personal-baseline logic stops being the right framing.

The Boiling Frog — Kreev's slow-decline detector

Quick changes are easy to feel — you know when you've had a bad night's sleep. The dangerous changes are the slow ones: your VO2 Max creeping down 3 points over six months, your sleep getting 20 minutes shorter every week without you noticing, your resting heart rate climbing 1 bpm a month. Each daily reading is within your normal variation, so nothing looks wrong in the moment — but a year later, you've moved.

This is the boiling frog problem, and Kreev runs a dedicated "boiling-frog detector" for it.

In the background, Kreev compares your recent 30 days against the 60 days before that. If a metric is meaningfully drifting away from where it used to sit, you'll see it surfaced on the Trends tab under the Long-Term Direction card (Sentinel) — "HRV moderately declining," "VO2 Max near baseline," "Sleep meaningfully improving."

The card compares your last 30 days against a 60-day reference window ending where those 30 days begin — 90 days end to end. It needs about 45 days of data inside that reference window before it will say anything, which works out to roughly 75 days of history — so it's the long-game surface. Because Kreev backfills 30 days of Apple Health data at install, someone who was already wearing their watch typically sees it appear around 45 days in, not 75. Once it's live, it's the card that matters most over a year. The morning briefing is the daily value; the boiling-frog detector is the strategic value.

A faster, daily version of the same idea lives on the History tab → Recurring Bottleneck card: if the same metric (e.g., sleep) keeps dragging your recovery below where it could be this month, that's where you'll see it.

VO2 Max: how Kreev estimates it

Kreev calculates your VO2 Max estimate itself, on your iPhone, from your heart-rate data, using the published Heart Rate Ratio method (Uth et al., European Journal of Applied Physiology, 2004). Once one of your workouts includes a hard, sustained effort, it uses the highest heart rate you've recorded within the last 12 months, so the estimate follows you as you age. Until then it uses a formula based on your age and sex. The app labels each estimate “Personalized” or “Formula-based”.

Two things to know. Kreev reads only 30 days of workouts when you install, so its record of your highest heart rate grows toward a full 12 months over a year of use. And if your age and sex aren't set in Settings, Kreev can't make its own estimate — the app then shows Apple Health's own reading, labelled “From Apple Health”.

It is an estimate, not a lab test — treat it as directionally trustworthy over months, and watch the trend rather than any single reading. For day-to-day intensity in any sport, the Strain score is the better read — it uses your actual heart rate from the workout regardless of activity type.

Where to find what

Today tab — Healthspan Index, recovery score, Strain, Recovery vs Strain, check-in, morning briefing, VO2 Max, This Week, Today’s Metrics, Activity. "Top Contributing Factors" now lives inside the Recovery score's own drill-down, under its Analysis tab.

Trends tab — per-metric charts (HRV, RHR, Sleep, Strain, VO2 Max, Respiratory Rate) grouped into Load & Longevity / Autonomic Health / Recovery & Sleep, plus the Long-Term Direction card. Load & Longevity leads the tab. Free: current-month charts. Sentinel: up to 6 months of history + the Long-Term Direction cards.

① "LOAD & LONGEVITY" section header. Leads the tab. Groups Strain, Fitness vs Fatigue, Steps, and VO2 Max — the metrics that quantify training stimulus and aerobic fitness.

② Long-term direction. One row per metric: an arrow and a verdict — near baseline (as here), or a drift such as declining moderately / meaningfully declining. A downward amber arrow is the boiling-frog signal: the metric is slowly drifting away from where it used to sit. Worth a closer look. Sentinel.

③ Fitness vs Fatigue. The balance between acute and chronic fatigue. This is an indication of fitness adaptation. Sentinel.

④ "AUTONOMIC HEALTH" section header. Groups HRV, Resting Heart Rate, and Respiratory Rate — the metrics that read your nervous system's state.

⑤ Long-term direction. "Near baseline" row. Horizontal grey dash + near baseline. The metric is in line with the prior 60 days — no notable drift in either direction. Boiling-frog detector. Sentinel.

⑥ Metric tile (e.g., HRV). Each tile shows the metric name, current value, a sparkline of recent trend, and a small delta vs your baseline. Tap any tile to open its drill-down chart.

⑦ "RECOVERY & SLEEP" section header. Groups your Recovery score and Sleep duration — the daily outputs of recovery.

⑧ Long-term direction. "Near baseline" row. Horizontal grey dash + near baseline. The metric is in line with the prior 60 days — no notable drift in either direction. Boiling-frog detector. Sentinel.

⑨ Sleep Consistency. Bed time consistency, an indication of variability affecting the circadian rhythm.

History tab — Free shows a preview: your most frequent recovery bottleneck and your strongest pattern, as headlines. Everything else — the VO2 Max & Aerobic Trend card, the six-month Healthspan Index trend, the Sentinel Pattern, the full Recurring Bottleneck detail, Your Patterns, the month-over-month Recovery & Strain and Autonomic Consistency cards, and the monthly heatmap archive — is Sentinel. "Your Patterns" needs about 60 days of data, so it appears around a month into use.

① VO2 Max & Aerobic Trend. Leads the History tab. Your VO2 Max over the last 30 days, its ACSM zone for your age and sex (here, Superior), and whether the estimate is Personalized (from your own measured peak heart rate) or Formula-based. On the right, the Aerobic Trend — whether your fitness is rising, holding (Stable, as here) or falling — with the change against 90 days ago. A short highlight sums up the longer picture, e.g. "Holding steady — 5 months inside a 1.9 ml/kg/min band." Sentinel — the free tier shows your latest VO2 Max number on the Today tab only.

② Month-by-month chart. One dot per month for your VO2 Max, with a bar behind each showing how far it moved within that month — so you can tell a real shift from ordinary month-to-month noise. Below it, a plain-English note on what changed: when you crossed into a new zone, and how far you are from where you sat 90 days ago. VO2 Max moves slowly; read this over months, not weeks. Sentinel.

③ Six-month Healthspan Index trend. Your Healthspan Index month by month, with its direction over the period shown — whether your five ageing markers are moving together or apart. Sentinel; the Index itself is free on the Today tab.

④ Sentinel Pattern card. A weekday bar chart showing your average recovery score for each day of the week, with the lowest-recovery weekday called out. Helps you spot patterns like "Mondays are systematically low because Sunday-night sleep is short." Free shows the headline weekday; the full chart is Sentinel.

⑤ Recurring Bottleneck card. Surfaces the single metric most often dragging your recovery score below the rest of the month, with above/below threshold comparison and percentage attribution. Free shows which metric it is; the detail is Sentinel.

⑥ Your Patterns card. Patterns Kreev has found in your own measured data — sleep vs next-day HRV, a hard day's strain vs next-day recovery, step count vs next-day strain, breathing rate before a lower recovery, your lowest weekday, bedtime regularity vs HRV, and (with the check-in) how you feel vs your scores. Associations, not causes. Needs 60 days of history, about a month of use. Sentinel; free shows your strongest pattern as a headline.

⑦ Recovery & Strain, month over month. This month's Recovery and Strain side by side, each with its change from the previous month, plus one sentence on what the pair means together — here, "Recovery and strain are in equilibrium — autonomic balance held steady from August into September." Not to be confused with the Recovery vs Strain chart on the Today tab: this card compares whole months. Sentinel.

⑧ Autonomic Consistency. How this month's days split across the four recovery zones — Peak, Baseline, Below and Critical — as one colour bar with a percentage for each. A month that is mostly green is a steady one; a growing amber or red share is worth a look before it shows up in your Archive. Sentinel.

⑨ Autonomic Archive. Up to six calendar-grid heatmaps — one per month, for your six most recent months — each colored by recovery score per day: cyan (Peak), green (Baseline), amber (Below), red (Critical). Lets you compare your current month against recent history at a glance. Sentinel.

Month in Review (not pictured). A monthly narrative on the History tab — the same plain-English interpretation as the daily briefing and Weekly Debrief, but summarizing your month once at least 5 days have scored. Sentinel.

Kreev on your Apple Watch

Sentinel. Kreev's watch app shows the same four numbers as your iPhone — Recovery, Strain, VO2 Max and your Healthspan Index — plus today's training context. Your iPhone does all the computing and sends only the finished scores to your watch, directly over Apple's own encrypted connection; the watch app has no access to Apple Health at all — nothing on your wrist to leak, and nothing goes over the internet to get there.

Adding Kreev to your watch face

Kreev offers five Apple Watch complications: Recovery, Strain, VO2 Max, Healthspan, and a Kreev brand mark for watch faces that only have room for one.

Add one on your Apple Watch itself:

1. Press and hold the display until Edit appears
2. Tap Edit, then swipe to Complications
3. Tap the complication slot you want to fill
4. Scroll to Kreev and choose the one you want
5. Press the Digital Crown to save

Use your Watch, not your iPhone, for this. Third-party complications like Kreev's can be unreliable or missing from the picker in the iPhone Watch app — a known watchOS limitation — even though they work correctly once added on the Watch itself.

Most faces support one to four complications, so you can mix and match. The Kreev brand mark renders on any tier — it shows the mark, not a reading, so there is nothing to withhold. On Sentinel, tapping it opens the combined Recovery / Strain / VO2 Max / Healthspan screen; on the free tier it opens Kreev's subscribe screen.

My complication shows a lock. The Kreev watch app and its Recovery, Strain, VO2 Max and Healthspan complications are part of Sentinel. watchOS lists every installed app's complications whatever your subscription, so you can add one on the free tier — it will show a lock until you subscribe. The Kreev brand mark works on any tier.

Guardian Alerts

Sentinel. A notification on your iPhone, evaluated by the app when it analyses new data — nothing is sent to or from a server — when your recovery state deviates significantly from your baseline: a heads-up outside your normal check-in time, not something you have to go looking for. The trigger thresholds are set by Kreev, not user-configurable; in Settings you control only whether the underlying score value is shown in the notification.

Settings — notification preferences (including the option to hide your score from lock-screen notifications for privacy), Show Score on Apple Watch (off shows the zone-coloured ring only, no number, for anyone who'd rather not have a figure visible on their wrist), Edit Profile (age and biological sex), Export My Data and Import My Data (your backup and restore), Restore Purchases (re-links a Sentinel subscription on a new phone), and Reset This Device (permanently erases everything on this iPhone and your Apple Watch — there is no account and no server copy).

Free vs Sentinel

Kreev runs entirely on your iPhone — no account, no sign-in, no server. Everything in this guide works offline. Sentinel comes with a 1-month introductory free trial through the App Store; after that, your core daily numbers stay free, and the interpretation layer — plus the Kreev Apple Watch app — is Sentinel.

Free tells you where you stand today. Sentinel tells you where you're heading.

Also free: the subjective check-in, the illness early-warning banner, and the 7 AM reminder.

What's new

See the full changelog for release notes.

Important: this is not medical advice

Kreev provides personal informatics and analytical insights — not medical advice or diagnoses. If a metric on Kreev concerns you, or your real-world symptoms don't match what Kreev says, see a doctor. Use Kreev to inform your training, sleep, and recovery decisions; use clinicians for medical questions.

Get in touch

This guide updates as Kreev evolves. If something isn't clear, or you've noticed something that doesn't match what's written here, write to us at support@kreev.app — your feedback shapes the next build.

— The Kreev team