Hey everyone,
Long-time Intervals.icu user here. I’ve been using it as my training hub for years, and it’s far and away the best platform for tracking fitness and recovery — especially with the wellness features.
The frustration
My training stack is Apple Watch + Intervals.icu. Garmin and WHOOP users get their wellness data synced natively. Apple Watch users don’t. Also, apps like HealthFit did not isolate HRV and resting HR from sleep. So every morning I was using a wonky shortcut script or either manually entering some wellness data when that broke and then going to intervals.icu to update subjective wellness fields… or just skipping it.
I wanted something dead simple: wake up, get a notification after I’m ready to think about how I feel, tap through the subjective stuff (soreness, fatigue, stress, mood, motivation), add some comments, and have everything else already synced from my watch automatically. No fiddling with settings, no extra screens to navigate.
What it does
IntervalsWellnessSync does one thing: gets your Apple Watch health data into your Intervals.icu wellness log.
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Automatic overnight sync — Sleep duration, sleep score, HRV, resting heart rate, weight, SpO₂, menstrual cycle tracking, and more. Pulled from HealthKit and uploaded directly to your Intervals.icu wellness fields. Note: HRV and resting heart rate are pulled from a sleep sessions only - you have to have Sleep | Wake Up time set-up in iOS sleep schedule.
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Morning wellness check-in — A notification each morning at a time you choose. Tap through sleep quality, soreness, fatigue, stress, mood, and motivation on a 1–4 scale. Done in 15 seconds.
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Enhanced HRV capture — An opt-in overnight mode that records beat-to-beat heart rhythm data from Apple Watch and computes rMSSD (the gold-standard recovery metric). Goes beyond Apple’s single spot-check SDNN reading. Uses a 3-stage artifact correction pipeline (Plews method) with median Ln(rMSSD) across 5-minute epochs.
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Sleep score — Computed from duration, sleep stages, continuity, efficiency, and heart rate — modeled after Apple’s approach.
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Per-metric exclusion — Already have a Garmin or Oura syncing certain metrics? Exclude those individually so nothing gets overwritten. The app fits into your existing setup.
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Manual Override - You can also manually override data. I find this useful when I sleep past my alarm and want to log that extra hour of sleep.
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Backfill Historic Data - There is a backfill tool in settings to add historic wellness data to interval.icu. I’ve built in a method to undo changes also. Test this carefully.
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Food Tracking - Macros and Calorie data from the previous day is updated in the morning sync and any current updates in data will propagate during the day if you sync. So if you add something you forgot to eat to your food tracker to the previous day it will update with any of the current days syncs.
Note: You can add and move wellness tiles to/on the homescreen.
How it integrates with Intervals.icu
Data flows directly from your device to Intervals.icu via the API:
Apple Watch → HealthKit → IntervalsWellnessSync → Intervals.icu API
Sign-in uses OAuth — you authorize through Intervals.icu, and your password never touches the app. No API keys to copy, no developer settings to dig through. Just tap “Sign in with Intervals.icu” and you’re syncing.
How this is different from Intervals Companion
Spencer’s Intervals Companion app is fantastic — it does a ton and the widgets alone are worth it. If you want widgets, graphs, a workout library, activity details, and a full mobile companion experience, use that.
IntervalsWellnessSync is deliberately simpler. It’s for the people who just want their Apple Watch wellness data flowing into Intervals.icu with zero fuss. No widgets, no graphs, no workout syncing — just health data in, wellness log updated, done. Set it and forget it.
Privacy
No analytics. No tracking. No ads. Your health data goes directly from your device to your Intervals.icu account over HTTPS. The auth server handles only the initial OAuth token exchange — no health data passes through it.
The HRV and sleep score algorithms are open source: GitHub
Pricing
Free on TestFlight right now: Join the IntervalsWellnessSync beta - TestFlight - Apple
Website: https://intervalswellnesssync.com
What I’d love feedback on
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Is the morning notification flow smooth, or would you change anything about it?
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How does the sleep score compare to what you see from other sources (Garmin, WHOOP, Apple)?
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Anything missing from the wellness fields that you’d want synced?
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Female athletes: The app syncs menstrual cycle tracking from Apple Health — I’d love to hear if this is working well for you and if the data shows up correctly in your Intervals.icu wellness log.
Big thanks to David for building Intervals.icu and for the excellent API — this wouldn’t exist without it.
Would love to hear what you think!
