How MyBodyAI works

What MyBodyAI is, and what it is not#

What it is#

MyBodyAI is a tool for understanding the trends in your own data. Each morning it answers a few plain questions: how did your body come out of the night, how heavy has your training been compared with your habit, is anything drifting away from your usual, and what would be a sensible thing to do today. The answers are built from sleep, heart rate, overnight HRV (heart-rate variability, the small beat-to-beat changes that reflect how rested your nervous system is), activity, stress readings, weight and a few more signals, depending on what your devices send.

The numbers come in three kinds, and the app keeps them apart:

• Indices. Twelve indices, each on a scale from 0 to 100 (Sleep Debt is also read in hours): Immunity, Recovery, Stress Load, Sleep Debt, Body Clock, Nervous System, Body Alert, Overtraining, Breathing, Morning Energy, Sleep Quality and Cardiac Fitness. Each has its own entry in this Encyclopedia.
• Summaries. Body Status (the state of the day in one word), Training Readiness, Training Balance and biological age.
• Plain readings. Steps, minutes, weight and the like, shown as your device or your own entry gave them.

What it is not#

The terms of service say it in so many words: the service is not a medical device, it is not intended for the diagnosis, prevention, monitoring, treatment or alleviation of any disease, and its indices are "algorithmic estimates derived from wearable sensor data". They are not clinical measurements and not medical diagnoses. See the terms of service, section 3.

In practice that means:

• A score is a signal to look at, never a verdict on your health. A high Body Alert means several of your numbers have moved away from your usual at once. It does not say you are ill, and a low one does not say you are well.
• Where the app talks about signs that often come with an infection or with overload, it says "worth a rest" or "worth keeping an eye on". If you feel unwell, or a number worries you, talk to a doctor. The app does not replace one.
• Safety alerts, such as a very low blood oxygen reading or a very high blood pressure reading, are there to prompt you to check and to seek care when you need it. They are not a diagnosis either. See Body Alert.

From your device to your scores#

Step by step#

1. Your device measures. The watch, ring or scale records heart rate, sleep, movement and the rest. Many measurements happen while you sleep.
2. Your device hands the data on. A watch syncs with its maker's app, which sends the data to the maker's cloud. On an Android phone, the watch app can also write into Health Connect, the health data store of the phone. This step belongs to your device and its maker. Nothing we do can make it happen faster.
3. We read them. For a connected service (Polar, Oura, Withings, COROS, Google Health, the Garmin link) we receive a notice or ask for new data, usually within about 30 minutes of the device's own sync. The MyBodyAI Android app reads Health Connect on the phone. A Garmin export arrives when you upload it. Devices lists every route and Sync gives the timings.
4. We keep one summary per day. For each calendar day we store what arrived: the night, resting heart rate, steps, stress, weight and so on, and each workout separately. A day counts as a "day with data" when it holds at least one of a set of readings: sleep length or score, resting heart rate, stress, steps, morning Body Battery, blood oxygen, weight, deep sleep or active minutes.
5. We compute the scores. The server reads your summaries, mostly of the last 30 days, some of the last 90 days or a year, and works out every index, the verdict, the advice and the day's sentences. The result is stored for the day, so history is quick to show.
6. The app shows it. The web app, the Android app, the widgets and the morning notification show the same stored numbers and sentences.

When two sources describe the same night or the same steps, one value is chosen by fixed rules, never added together. See Sources and overlap.

Where the computing happens#

Every score, every verdict and every sentence about your body is computed on our server from your stored data. The app and the website draw what the server sends. That is the reason the phone, the browser and the widgets agree, and the reason a new version of a calculation reaches everybody at once.

Some screens add up what you ask them to, for example the average of the days in the period you picked on the Trends tab, or the sum of your minutes on the Activities tab. That is arithmetic for display, on numbers the server already computed.

The sentences are put together from templates and rules in our own code, filled with your numbers, which is why the card titled "AI insights" reads the same way the rest of the app does. See the questions at the end of this page.

Whose day it is#

Days follow the time zone saved in your profile. A night belongs to the day it ends on. Today's numbers are worked out with what has arrived so far, so they can still change during the day, and the app says "Provisional" where the verdict still stands on a night that has not arrived (see why a past day can change).

Your personal normal#

What a normal is#

A number means little by itself. A resting heart rate of 58 is high for one person and low for another. So most scores are read against your own recent normal: the middle of your own numbers over a window of days, and how far they usually swing around it. General tables by age and sex stay in the picture where a body-wide reference exists (for example the sleep a person of your age needs), but the question the app asks most often is "is today unusual for you?".

The windows#

Each quantity has its own window, because it moves at its own pace. These are the main ones:

Two more details. The "usual" for sleep and resting heart rate is the mean of your own earlier days, and the usual range is one standard deviation either side of it, which is the span that about two days in three fall inside. The scored day is left out of its own reference, so a bad night cannot widen the range it is judged by. The HRV band is half a standard deviation either side of your baseline, the smallest change research treats as worth noticing. See HRV, heart rate and the nervous system for the full rule.

When the normal is ready#

The usual for sleep and resting heart rate needs 7 earlier days, so with a brand new device it exists from the eighth night at the earliest. When your devices bring history with them (about three months from most services), it is ready on the first sync. The first time it is ready, the Overview shows one card, "Your normal is ready", with a line such as "We worked it out from your last 12 nights (sleep and resting heart rate)." that names the number of nights actually used, and adds "and several weeks of HRV" when your HRV baseline exists. The card appears only in the first 14 days of your data, only once, and closing it with the cross keeps it closed on every device of your account.

The HRV baseline needs 7 weekly averages, which nine nights in a row provide, because the weeks overlap. The HRV band is stricter and needs your nights to span 28 days. Until then the HRV card says it is learning your band.

Where you see it#

• On the Body Status dial, "Your usual 52 to 66" with a ring for yesterday (Body Status).
• On the Sleep tab, where the overnight signals are drawn with your usual range and a ring marks a night outside it (Sleep Quality).
• On the HRV card, where your week sits against your band (HRV).
• In "Load vs. usual" on the Activities and Performance tabs (Training load).
• In many sentences: "below your usual", "above your usual band".

Measured and estimated#

How the app marks it#

A measured number is one a device or an app recorded: your resting heart rate, your night's length, your steps. An estimate is a number we compute from measured signals because no device reads it directly. The app marks the difference wherever it matters:

• A small chip next to a number says where it came from: "measured" with the device's name, "estimate" or "your entry". See Sources and overlap.
• Tiles and factors that are estimates carry "(estimate)" and the tooltip "An estimate from your signals, not a direct measurement" (Czech “Odhad z Vašich signálů, ne přímé měření”). Morning Energy is an example when you have neither a Garmin watch nor an Oura ring (Morning Energy).
• On the Activities tab calories read "estimate" or "from device", and "Body load" is an estimate from your mix of activities.
• VO₂max is shown as "estimated", with its date, because no wearable measures it directly.
• The energy map of the day and the "What if" panel are models of a typical day built around you, and they say so.

A "Data quality" chip with a percentage appears beside the verdict only when it is under 50%. It says how many input signals we have for the past week, not how accurate they are. A low number means data are missing, not that a score is wrong.

Missing data and zero#

A zero a device reports is a measurement. A missing value is not zero. Scores and averages leave a missing value out instead of counting it as nothing, and a score that cannot be computed is not shown at all, so you never get a made-up number. A tile that has no number says why:

• "Collecting data (2 of 3 days)" means the score needs a few more days of history. Most scores need 3 days. Cardiac Fitness, Overtraining and Body Clock need 7.
• "Your device does not measure this" means no connected device sends the signal the score is built on.
• "No current data" means the signals existed but have aged out. The card then names the day they last measured.

Values that cannot be right (a resting heart rate of 20, a sleep of 20 hours) are refused before they reach any score. See Sources and overlap.

Scores, words and colors#

Scores run from 0 to 100, and a higher number is better. Where a raw index runs the other way (Body Alert, Stress Load, Overtraining), the app shows its positive name on summary cards: Resilience, Calm and Freshness. The word beside a score comes from ten bands: Critical (0 to 10), Concerning (11 to 20), Weak (21 to 30), Low (31 to 40), Slightly low (41 to 50), Balanced (51 to 60), OK (61 to 70), Good (71 to 80), Very strong (81 to 90) and Elite (91 to 100). The color follows the same ten bands.

A score that sits right on the line between two bands would flip its word from day to day. So the word changes only after the score has cleared the new band by 3 points. A move across several bands lands on the band it truly reached, so a real change is never held back.

The calculation version#

Every calculation carries a version. When we improve how a number is computed, for example after new research or a better rule for a rare case, we raise the version. The version is not shown in the app and you do not need to know it.

What a new version does:

1. New days are scored with the new rules from that moment.
2. Days already stored with the old version are scored again, overnight, by a pass that walks through your whole history. A sync recalculates the last 90 days, so the overnight pass is what reaches older days. A pass leaves your account alone while a sync is running and comes back to it a little later.
3. If the new rules move a number you had already seen by 5 points or more, the Trends tab tells you (see below).

The point of a single version is that all your days are always scored by the same rules, so a chart is never a patchwork of two methods. The cost is that an old day can change, which is the next section. The entry Sync describes the overnight pass.

Why a past day can change#

A day you have seen can be scored again. There are five reasons, and none of them is you doing something wrong:

1. Late data. Data reach us late as a matter of routine. A night written into Health Connect when the watch next syncs with the phone, or a Garmin export uploaded days later, brings a day that was scored without it. Until the night arrives, the day is scored with your usual night and marked "Provisional", and it is scored again when the real night comes. That stand-in is used only for today and yesterday, only when the whole night is missing, and only when your device delivered that value on at least 4 of the 7 days before. See Body Status.
2. A new version of the calculation, as above.
3. A Garmin export or new data from your Garmin link, which can bring older nights.
4. A change to your activities. Adding, editing, deleting or restoring a workout recalculates from that day on, because load and recovery read a rolling window.
5. A change to your profile. A new date of birth, a new sex or a new maximum heart rate you entered changes the targets each day is scored against (for example the deep-sleep share and the heart-rate ceiling), so the past days are scored again. The field for your maximum heart rate says it: "A change recalculates past sessions too".

The line on the Trends tab#

When a recalculation moves a score you had already seen by 5 points or more, the Trends tab shows a quiet line under the title. It names the day the pass ran, how many days of history moved, and why, for example "5/11: 3 days of history recalculated (a Garmin data import)." with the link "What changed". The reason is one of "a new version of the calculation", "a Garmin data import", "a change to your activities", "a change of age, sex or maximum heart rate in your profile" and "data from your linked Garmin". A tap on "What changed" lists the days, each with the old and the new value, for example "2/11 · Recovery: 78 → 69". The line shows the newest recalculation of the last 30 days, and the records behind it are kept for 180 days. Smaller moves are rounding and are not listed, and a day that settles after its night arrived is not counted as a revision.

Opening a past day#

The calendar on the Overview, Health, Sleep, Activities and Performance tabs opens a past day. The tab then works the day out again from the data we hold now, using only the days up to that date and the rules of the current version. The colors in the calendar itself (the Body Status of each day) and the charts on the Trends tab are the stored values. In rare cases the two can differ for the same day, for example while a recalculation is still on its way, and the next pass brings them together. See the app tour.

The first days and weeks#

Day one#

Until a source is connected and a first score exists, the Overview shows a short guide, "Get started with MyBodyAI", with three steps: "Connect a device", "Syncing your data" and "Fill in your daily check-in". A line shows how many are done ("1 of 3 steps completed"). While the guide is up, the step "Syncing your data" says "Data syncs automatically. From most sources it arrives within 30 minutes; with the direct Garmin link, a few minutes after your watch next syncs with Garmin Connect." After you connect a service, a banner says, for example, "Fetching your Polar data, this usually takes up to 30 minutes" and, once it lands, "Your Polar data has arrived. Reload the page if you do not see it yet." The Garmin link starts on the day you link it and does not bring older days, so the banner there says it is waiting for your watch to sync with Garmin Connect. An export fills in the older ones.

The 7-day Premium trial starts on the first day measured data reach your account, not on the day you register. See plans.

The first nights#

• After about three nights, the first scores appear. Most indices need 3 days of history. A single night is not enough for most of them. Body Status needs at least 5 of its 12 signals and a night in the last 7 days. Until then it says "Insufficient data" and tells you why (Body Status).
• From 7 days, Cardiac Fitness, Overtraining and Body Clock appear, and your usual for sleep and resting heart rate is ready (from the eighth night if you started from nothing).
• After about four weeks, your HRV band appears, because it needs nights that span 28 days.
• After 30 days, your usual covers a full month, which makes it steadier, and, as the first-run screen puts it, patterns in your behavior have enough data to mean something.

Everything that needs history arrives sooner when your devices bring their own. About three months come with most services at the first sync, and Health Connect brings 30 days or, with your consent, 90.

Which tabs show up#

A tab that your devices could never fill is left out of the menu: Sleep, Activities, Performance and Trends can disappear for an account whose devices do not send what they show. This starts only after 14 days of data. See the app tour.

Privacy in one paragraph#

Your health data are stored primarily on servers within the European Union and used to compute your scores. We never sell your personal data, and we do not share your health data with advertisers, insurance companies, employers or other third parties for commercial purposes. You decide which devices are connected, and you can disconnect any source in Settings at any time. Who sees what, how to export your data, how to delete your account and the consents we ask for are in Privacy and your data, and the binding text is the privacy policy.

Where each question is answered#

• Your day in one word: Body Status. Energy through the day: Morning Energy.
• Rest and training: Recovery and Training Readiness, Training load, Heart-rate zones, Daily coach, Training plan, Activities.
• Heart and body: HRV, heart rate and the nervous system, Stress, Body Alert, Biological age.
• Sleep: Sleep Quality, Sleep need, debt and rhythm.
• Data: Devices, Sync, Sources and overlap, Troubleshooting.
• The app and your account: App tour, Progress, Energy pacing, Plans, Settings, Notifications, widgets and the watch.

Frequently asked questions#

Is MyBodyAI a medical device?#

No. It is a wellness app. It does not diagnose, treat or monitor any disease, and its scores are algorithmic estimates, not clinical measurements. Use it to notice trends and to decide how hard to train or how much to rest, and see a doctor for anything medical. The wording is in section 3 of the terms of service.

Why do I see no numbers yet?#

Either nothing has arrived, or too few days have. Data usually take up to 30 minutes after your device syncs with its maker's app, and a Garmin link waits for your watch to sync with Garmin Connect. Most scores then need 3 days, and some need 7. Open the tile: it says "Collecting data (2 of 3 days)", "Your device does not measure this" or "No current data". The first-days list above says what appears when, and Troubleshooting walks through a source that stays silent.

Why did yesterday's number change?#

Because something it stands on reached us after you looked: a night that arrived late, a workout you edited, a new version of the calculation, a Garmin export, or a change to your date of birth, sex or maximum heart rate. A move of 5 points or more is named in the line under the title of the Trends tab, with the old and the new value. See why a past day can change.

What does "estimate" next to a number mean?#

That the number is computed by us from measured signals, and no device read it directly. A resting heart rate your watch measured is "measured". Morning Energy on a phone without a Garmin or Oura is an estimate. We show the difference so that you do not read a model as a measurement. See measured and estimated.

Where are my numbers computed, and does the app do any maths?#

On our server. The app only draws what the server sends, and does simple arithmetic for display, such as the average of the days you picked. That is why the web app, the Android app, the widgets show the same figures.

Does a chatbot write the sentences in the app?#

No. The sentences, including the card titled "AI insights" and the story of the day, are put together from templates and rules in our own code, filled with your numbers.

How long until my normal is ready?#

If your devices bring history, on the first sync, because the usual for sleep and resting heart rate needs 7 earlier days. Starting from nothing, from the eighth night. Your HRV band needs nights spanning 28 days. The details are in when the normal is ready.

Does MyBodyAI read my data from before I joined?#

Yes, for your scores. Most services hand over about three months at the first sync, a Garmin export up to 90 days, and Health Connect 30 days or 90 with your consent. Those days feed your normal and your history. They do not count toward XP, streaks or badges, which start on the day you register (Progress).