Garmin → Intervals.icu Bridge

Garmin started filtering the FIT files it sends to Intervals.icu. This puts the data back — and syncs a lot more.

TL;DR — Since late September 2026 Garmin strips its own metrics (Stamina, Recovery Time, VO₂max, Performance Condition, Training Effect, Sweat Loss …) from the FIT files it sends to Intervals.icu. This tool fetches the original file from Garmin Connect and adds the missing data to the activity the official sync already created — no duplicates, nothing deleted, training load untouched. It also syncs the daily wellness data the official sync misses (night SpO₂, respiration, sleeping HR, Body Battery, HRV details, sleep stages, stress, readiness, logged nutrition and total burn, endurance & hill scores, race predictions, fitness age, Health Snapshots …), puts your Garmin gear (bikes, shoes, skis) on the activities, can write ImReady4's daily training advice for you, backfills the past, and comes with 20 charts for all of it in Intervals' chart library. Runs on Linux (systemd timers), in a container, or on Windows or a Mac with a few copy-and-paste commands (guides for Windows, Mac and Synology).

_{An officially imported run after the bridge: Training Effect, VO₂max, Performance Condition, Recovery Time, Stamina at start/end, Sweat Loss — all stripped by Garmin, all back.}

_{A custom stream (grade-adjusted speed) written into the same activity, aligned by timestamp.}

_{Three of the twenty charts from the chart library: sleep stages, stress & Body Battery, intake vs. total burn.}

Since the end of September 2026 the file Garmin hands to partners is not the file your device recorded. (Garmin first switched the filter on in March 2026, rolled it back after a week of protest, and switched it back on half a year later.) The recording survives (power, heart rate, GPS, cadence, developer fields); Garmin's own metrics do not. Open the same activity in Intervals.icu and in Garmin Connect and you will miss Performance Condition, Stamina, Recovery Time, VO₂max, Training Effect and Sweat Loss. The original file you can download from Garmin Connect still has them.

This bridge is a small self-hosted service that:

• fetches the original FIT through Garmin Connect's private API, byte-identical to the browser export;
• finds the activity the official sync already created in Intervals.icu — the sync stays on, nothing is duplicated, deleted or recomputed;
• adds exactly what Garmin stripped, into the custom fields and streams you have configured (Stamina curve, Recovery Time, VO₂max, Performance Condition, Sweat Loss, Training Effect …);
• fills the daily wellness values the official sync does not deliver: night SpO₂, respiration, sleeping heart rate, Body Battery, HRV details, sleep stages, stress, readiness, floors, scale data — and your logged nutrition (kcal, carbs, protein, fat);
• can backfill the past (on the reference account SpO₂ had silently stopped arriving in mid-2025);
• reacts within about a minute of the official import, with Garmin contacted only when there is something new.

Everything is a dry run until you say --apply. Values that exist are never overwritten unless they demonstrably came from a filtered file.

Sister project: the Futureweb Intervals MCP lets ChatGPT, Claude and any other MCP client read and analyse everything the bridge writes: every custom activity field and stream, every native and Garmin… wellness field, with the names and units of your own definitions. Install with uvx futureweb-intervals-mcp@1.0.0b1, from Docker Hub or as a Claude Desktop bundle; more below.

What gets synced

Version 0.7.0. Verified end to end on one account (fenix 8, Edge 1040); the first live writes and the evidence are recorded in docs/PLAN.md.

How it works

1. Original FIT. garminconnect downloads the activity's original export; the ZIP is unpacked in memory, the FIT is CRC-checked with Garmin's official FIT SDK and archived unchanged.
2. Match. The Intervals activity is found by external_id (the official sync stores the Garmin activity ID) or, failing that, by source, start time (±120 s) and duration (±5 %). Anything ambiguous is left alone.
3. Gap. The file Intervals received (GET /activity/{id}/file) is decoded next to the original. What only the original carries is the gap: whole message types, record fields (stream candidates), session fields (scalar candidates), developer fields, and Garmin-internal numeric IDs.
4. Write back. Your own custom items say what to write and from where. Intervals fills custom activity fields and custom streams from the FIT itself, and every definition names its source (fit_session_field: "140.9", fit_record_field: "stance_time", or a one-line script reading m.f_138), plus an optional first-import conversion. The bridge reuses those definitions verbatim: same fields, same source, same units, nothing Garmin-specific hard-coded. Scalars go through PUT /activity/{id}, streams through PUT /activity/{id}/streams, aligned to the activity's time stream by timestamp.
5. Never overwrite real data. An existing value is replaced only when its FIT source is present in the original and absent from the partner copy; then it cannot have come from data (Intervals stores 0 for a stripped source). A second run writes nothing.

Garmin does not filter every activity. The gap is measured per activity and never assumed.

Quick start

Python 3.12 or newer.

python3 -m venv .venv && . .venv/bin/activate
pip install -e '.[dev]'
pytest -q                                   # synthetic tests, no accounts needed

export INTERVALS_API_KEY=...                # Intervals → Settings → Developer
export INTERVALS_ATHLETE_ID=0               # 0 = the key's owner
export BRIDGE_DATA_DIR=./data               # FITs, raw JSON, SQLite, tokens

garmin-intervals-bridge login               # once, interactive, MFA supported; stores tokens only
garmin-intervals-bridge probe               # newest original FIT, archived; no Intervals access
garmin-intervals-bridge gap --activity-id <garmin id>      # what did Garmin strip? read-only
garmin-intervals-bridge enrich --activity-id <garmin id>   # dry run: the exact plan
garmin-intervals-bridge enrich --activity-id <garmin id> --apply

Then let it run on its own:

garmin-intervals-bridge watch --apply       # one cheap Intervals poll; Garmin only on new activities
garmin-intervals-bridge sync --apply        # full run over the last days, activities + wellness

Everything is a dry run until --apply is given. The plan printed by a dry run is exactly what --apply would send.

Commands

Modes

enrich (default). The official Garmin import stays on. Each imported activity is completed with what its file lacks. This is the mode for everyone who wants to keep Intervals' own import, training load and workout pairing.

upload (--mode upload). The v0.1 behaviour for accounts that switched the official activity import off: originals are posted as new activities, guarded by a persistent pending state so a timed-out upload is never replayed blindly, and blocked when an activity already exists nearby. Intervals de-duplicates uploads by file hash, so with the official import on this mode would create duplicates. Use it only with the import off.

Wellness

Garmin's daily endpoints (sleep, HRV, stress, Body Battery, readiness, respiration, SpO₂, hydration, scale, nutrition, intensity minutes, scores, predictions, fitness age, lactate threshold, …) are fetched per day; every raw response is archived as JSON. Values are written to Intervals only where the day has nothing yet, locked days are skipped, and running totals of the current day wait for tomorrow.

When Garmin is asked: on evidence, not on a clock. Today's values come from nine endpoints (sleep, HRV, Training Readiness, scale and Garmin's status metrics) and only exist once the watch has synced after you wake up. Every ten minutes the bridge looks at Intervals' own record for today, which costs no Garmin request; as soon as the official integration has put last night's sleep there, it reads those endpoints once, typically within ten minutes of the watch sync, and asks twice more for Training Readiness if that lags behind. Recovery time, acute load, endurance and hill scores, cycling VO₂max, fitness age and race predictions arrive in the morning as Garmin sees them then; the day's final read replaces them with the evening's. A finished day is read in full once the device has synced after it ended, so its totals are complete; a night-time phone sync is enough. Without the official wellness sync, Garmin itself is checked at a few fixed times in the morning, and a day that never sees a sync is read anyway at 20:00 the day after. A normal day costs about 80 Garmin requests, plus a few per new activity.

Native Intervals fields filled when empty: restingHR, hrv, sleepSecs, sleepScore, readiness, vo2max, steps, floorsClimbed, hydrationVolume, spO2, respiration, avgSleepingHR, weight, bodyFat, and from logged food kcalConsumed, carbohydrates, protein, fatTotal. Everything else goes to private custom fields named Garmin…, listed in docs/FIELD_MAPPING.md. BRIDGE_WELLNESS_PROFILE=recommended (default) leaves out a handful of duplicates and goals; all keeps every code.

Backfill the past when the official sync has gaps (on the reference account SpO₂ stopped arriving in mid-2025):

garmin-intervals-bridge backfill --scope wellness --from 2025-01-01            # dry run
garmin-intervals-bridge backfill --scope wellness --from 2025-01-01 --pause 3 --apply

A backfill uses the twelve per-day measurement endpoints by default (--endpoints all for every endpoint), pauses between days, and skips days already fetched, so it can be interrupted and resumed.

Gear

The official sync does not pass gear to Intervals. The bridge keeps each activity's gear (bike, shoes, skis …) in its archive anyway, so gear puts it on the Intervals activities without a single Garmin request. Intervals then counts distance, time and its gear reminders itself, and a bike's components follow the bike. The bridge never writes to Garmin and never removes gear from Intervals.

garmin-intervals-bridge gear                    # the plan: pairs, gaps, conflicts; writes nothing
garmin-intervals-bridge gear --create --apply   # create missing gear in Intervals, fill the gaps

In a container, next to the running bridge: docker exec <container> garmin-intervals-bridge gear … (it does not wait for the running bridge).

• Gaps (Intervals has no gear on the activity, Garmin has) are filled whatever you choose.
• Conflicts (both have different gear) follow --prefer: intervals (default) keeps Intervals' — its auto-assign rules or your corrections; evidence takes Garmin's only when the record proves Intervals' wrong: that gear was not bought yet or already retired on that day, or the bike's own sensors (Di2, power meter … by serial number, learned from the rides both sides agree on) are not in the recording; garmin always takes Garmin's. Every conflict is listed in the plan, with the proof where there is one. The first --prefer evidence run reads the sensors of every archived ride once (a few minutes; cached in gear-sensors.json).
• Pairs are found by name (Grail CF SLX 8 Di2 = Canyon Grail CF SLX 8 Di2); different names are paired with --map 'GARMIN NAME=INTERVALS NAME'. Gear Intervals does not have is listed, or created with --create (retired gear only with --include-retired).
• Totals: Intervals adds each assignment to a gear's totals, but totals that drifted earlier (reassignments by hand) stay off, and it computes a recount without storing it. So after writing, the bridge stores Intervals' own recount for the gear it touched and their components; --recalc does that for all paired gear (dry run first: the plan shows each change). Intervals counts a gear only from its purchase date; the plan lists activities that carry gear from before it was bought (an older pair?).
• Afterwards the scheduled runs keep the last week in line with the same choices. Gear chosen on the watch comes with the activity; gear picked in the Garmin Connect app after the run is read once more half a day later.
• History: the bridge knows the gear of the activities in its archive — those since it started, plus what backfill --scope activities --from DATE --archive-only adds once (a few Garmin requests per activity; stop a running container for it). Activities from Strava cannot be changed through Intervals' API and are left alone.

Training advice (ImReady4)

If you use ImReady4 (by @Inigo_Tolosa and @MedTechCD) for HRV-guided training, you know the morning routine: open MATLAB Mobile, run the script, and it writes Rest, LIT, Planned or HIT into the TrainingAdvice wellness field. With BRIDGE_IMREADY4_ENABLED=true the bridge does that step itself, a few minutes after your watch's morning sync has brought last night's HRV and resting heart rate into Intervals: same inputs, same 30-day z-scores, same zones, same field, so your existing chart keeps working. It reads Intervals only, writes only an empty TrainingAdvice (never one you or the script set, never a locked day), and writes nothing when the night's values or enough history are missing. garmin-intervals-bridge imready4 shows today's advice with its reasoning, compares past days with what the field already holds, and fills days that have none. It is off by default. On the reference account it agrees with ImReady4's own results on 97.6 % of 1,225 days; the details, the differences and how to set it up are in docs/IMREADY4.md.

Experimental, next to it: BRIDGE_HRVTREND_ENABLED=true writes a second advice into a field of its own, HRVTrendAdvice, from the 7-day HRV trend against a 60-day normal range and the night's heart rate, as the HRV-guided training studies did – calmer than the single-day score, meant for comparing both side by side. It never touches TrainingAdvice; see docs/HRV_TREND.md.

Charts

The bridge's twenty fitness charts are published in Intervals' chart library: Fitness page → a tab → custom charts → search for Garmin Bridge and tick what you want: readiness & recovery, sleep stages, sleep score & sleeping HR, SpO₂ & respiration, stress & Body Battery, HRV detail, nutrition intake vs. burn, macro energy, energy balance per week and month with weight, endurance & hill scores, VO₂max & fitness age, race predictions, intensity minutes & sweat loss, hydration, steps, body composition, skin temperature, Health Snapshot. Each is built from the fields the bridge writes, with one axis per unit and values that hold until the next measurement carried across the days in between.

Prefer your own copies? setup-charts --apply creates the same charts as private items in your account, only with the fields that already exist, and completes them later as fields appear (for example after a backfill with every endpoint). Charts you made yourself are never touched, even with the same name. Intervals' API cannot place a chart on a Fitness tab; that last click is yours either way.

Use it with an AI coach (MCP)

The sister project Futureweb Intervals MCP lets ChatGPT, Claude and any other MCP client coach from everything the bridge writes: Stamina per interval, Training Effect, Recovery Time, VO₂max, running dynamics, sleep and HRV details, fueling and sweat loss, read with the names and units of your own fields and set against your personal baselines. It talks to the Intervals.icu API only, never to Garmin, and is read-only by default. Until the bridge has written this morning's values, the MCP reports them as "not yet available" rather than as missing or zero; each project also works without the other.

uvx futureweb-intervals-mcp@1.0.0b1                                                  # from PyPI, starts on stdio
docker run --rm -i -e API_KEY=... -e ATHLETE_ID=i123456 futurewebat/futureweb-intervals-mcp:1.0.0b1

Claude Desktop: open futureweb-intervals-mcp-1.0.0b1.mcpb from the release page. GitHub · PyPI · MCP Registry · how it reads the bridge's data

Running it

systemd (recommended, no container): an unprivileged service user, a one-minute watch timer and a 30-minute full run, secrets in an EnvironmentFile, hardened units. See deploy/README.md.

Windows, macOS or any PC without systemd: pip install garmin-intervals-bridge (it is on PyPI), then garmin-intervals-bridge run --apply (on Windows py -m garmin_intervals_bridge run --apply, which Smart App Control does not block) keeps polling Intervals every minute, does a full run every 30 minutes and a health probe once a day, all in one process. Step-by-step guides for non-technical users: Windows, Mac.

Upload mode: when the official import is off

Garmin's partner terms now bar Intervals from passing Garmin-sourced data on through its own API, and Intervals has said it will probably have to block that. Data you upload yourself is not affected. The bridge's upload mode is built for exactly this: switch the official Garmin import off in Intervals, and the bridge uploads the original, unfiltered FIT of every new activity as your own file (source: UPLOAD, external_id: garmin:<id>). Intervals then computes everything from the complete file itself: Stamina streams, Recovery Time, VO₂max, Performance Condition, Training Effect, Sweat Loss and your other custom items appear without any enrichment, and no icu_intervals_edited flag is set. Wellness works the same in both modes.

garmin-intervals-bridge sync --scope activities --mode upload --activity-days 2          # dry run
garmin-intervals-bridge sync --scope activities --mode upload --allow-activity-upload --apply
garmin-intervals-bridge run --mode upload --apply       # keeps polling Garmin every 10 minutes
garmin-intervals-bridge backfill --scope activities --mode upload --from 2026-01-01 --apply   # the past, as your uploads
garmin-intervals-bridge backfill --scope activities --from 2026-01-01 --archive-only     # mirror first, upload later

Uploads are de-duplicated against what Intervals already has (external id, file hash, start time) and never retried blindly: an upload with an unknown outcome stays pending until you check. Systemd users swap the watch timer for deploy/systemd/garmin-intervals-bridge-upload.timer (10 minutes) and keep the 30-minute unit for wellness.

Docker / Podman: a ready-made image is on the GitHub Container Registry, ghcr.io/futureweb/garmin-intervals-bridge, and on Docker Hub, futurewebat/garmin-intervals-bridge (for NAS boxes whose container manager only knows Docker Hub, e.g. Synology – step by step in docs/SYNOLOGY.md). Tags latest and the version, amd64 and arm64. It runs as a non-root user and takes the same environment variables; without compose:

docker run --rm -it -v $PWD/data:/data -e INTERVALS_API_KEY=... -e BRIDGE_TIMEZONE=Europe/London ghcr.io/futureweb/garmin-intervals-bridge login
docker run --rm    -v $PWD/data:/data -e INTERVALS_API_KEY=... -e BRIDGE_TIMEZONE=Europe/London ghcr.io/futureweb/garmin-intervals-bridge sync --apply

BRIDGE_TIMEZONE is your own zone (Europe/London above is an example): a container has no time zone of its own, and the zone decides which date last night's sleep and a day's totals belong to.

cp .env.example .env            # fill INTERVALS_API_KEY
mkdir -p data && chown 10001:10001 data
docker compose pull             # ghcr.io/futureweb/garmin-intervals-bridge (amd64 + arm64); or: docker compose build
docker compose run --rm bridge login
docker compose run --rm bridge enrich --activity-id <garmin id>
docker compose run --rm bridge sync --apply

login is the one interactive step: run --rm gives it a terminal, it asks for your Garmin e-mail, password and MFA code, uses the password once and keeps only Garmin's session tokens in the mounted data/ volume (data/tokens), where they refresh themselves for about a year. Every other command just uses those tokens. If Garmin answers the login with 429, wait an hour and try again.

The compose service is deliberately not an always-on daemon; schedule docker compose run --rm -T bridge watch --apply from cron or a timer, or run docker compose run --rm -T bridge run --apply as a long-lived process.

Configuration

Variables can also come from a .env file in the working directory (or the file named by BRIDGE_ENV_FILE); variables already set always win.

Known limitations

• Garmin's endpoints are private and undocumented. They can change, rate-limit or block without notice. The mobile login path answers 429 for some clients; the web path with MFA works. Keep request delays.
• Writing streams marks the activity's intervals as edited (icu_intervals_edited = true, not resettable through the API). Intervals then no longer regenerates that activity's intervals on re-analysis. Harmless for an imported activity whose laps exist, but permanent. Writing scalar fields does not trigger it.
• Only definitions the bridge can read safely are used. Field scripts of the forms activity.X / 60, activity.X == 0 ? NaN : activity.X / 36 and stream scripts reading one m.f_<n> with constant factors are understood; anything else is listed as unsupported and left alone.
• Manual activities (no device file) are skipped. Strava-sourced activities are never touched.
• One Garmin account and one Intervals athlete per data directory.
• Intraday series (stress, heart rate, Body Battery curves) have no place in Intervals' one-value-per-day wellness model; they stay in the raw archive.

Troubleshooting

Security and privacy

Read SECURITY.md. In short: no passwords stored, tokens and the API key readable by the service user only, the data directory is personal (routes, health data) and must never be committed or shared, dry run by default, no deletions ever.

Legal note

• The bridge signs in to Garmin Connect with your credentials and reads your data through the same private endpoints the Garmin Connect web app uses. Garmin offers no official API for personal use, and Garmin's Terms of Use prohibit automated access to the site. Using this tool is your decision and your risk; the consequence Garmin's terms provide for is suspension of your Garmin account. No such case is known for any of the long-standing open-source Garmin clients, but there is no guarantee.
• Keep the load modest. The defaults – one download per new activity, a few wellness reads a day, paced backfills – make the bridge behave like a person using the site. Don't shorten the pauses to hammer the API; it would hurt everyone using tools like this one.
• Everything the bridge fetches stays on your machine. Nothing leaves it except what you choose to write into your own Intervals.icu account.
• In the EU, the Data Act (Regulation (EU) 2023/2854) and the GDPR give you a right to the data your device generates; this tool is one way of exercising it for your own use.
• Independent hobby project: not affiliated with, endorsed by or supported by Garmin Ltd. or Intervals.icu. Garmin is a trademark of Garmin Ltd.; names are used only to describe compatibility. MIT licence: provided as is, without warranty of any kind.

Acknowledgements

cyberjunky/python-garminconnect, Garmin's FIT SDK, the Intervals.icu API, and the forum thread that documented the problem.

MIT licensed.