Lactic BETA
The open-source training platform.
A training plan that fits your week, workouts on your smart trainer, and your recovery in one place.
Free, on your computer, with the AI coach of your choice. Or none.
Lactic is in beta. Expect a few rough edges, and please open an issue or use Send feedback in the app when something's off.
Download · MIT licensed · lactic.fit · Build from source · Contributing
- A plan that fits your life. Your goal, the time you have each day, and the weeks to get there.
- Every interval on target. ERG on your smart trainer, road mode for sprints, an overlay on top of Zwift or anything else.
- Train for the day you're having. A morning recovery score from your watch, and a plan that adjusts to it.
- A coach that knows your numbers. Built-in, the AI app you already use, or none. It suggests; you apply.
Free and open source. Your data stays in one file on your computer.
What it does
Every morning, one screen
Your recovery, your weight and how you feel. Today's workout, with Ride it one click away. Your form, your last ride, and a new FTP estimate when your rides call for one.
Rides that hold the watts
Lactic sets the watts for every interval and drops to road mode for sprints. The workout starts with your first pedal stroke, and paired gear reconnects on its own.
The overlay keeps the workout on top of other windows, full screen included: Zwift, a video, a browser. Want more at the end? Extend with a free ride, a held ERG target or another block.
Plans that adapt
Pick a goal (an event, a higher FTP, getting fitter or staying consistent) and the time you have each day. Lactic builds the phases and recovery weeks, forecasts your fitness to the end, and adjusts each morning for sleep, HRV and how yesterday felt.
Click a day to change it or ride it outside. Drag it to swap days.
Progress you can trust
Fitness, fatigue and form. FTP from critical power, your power curve and profile, VO2 max. All calculated on your computer by an engine with tests behind it. Compare any range with the one before, or with last year.
Recovery from the watch you already wear
A daily recovery score from sleep, HRV and resting heart rate, plus sleep stages and weight. Click any number for its history.
| Your device | How it gets to Lactic |
|---|
| Apple Watch | The Lactic Shortcut on your iPhone saves your nights to a synced folder (iCloud Drive, Dropbox, Google Drive, Nextcloud or Syncthing). Lactic picks them up. |
| Garmin, Oura, WHOOP (and Polar, Coros, Suunto) | Link it to intervals.icu, then connect intervals.icu to Lactic. |
| Android (Samsung, Pixel Watch, Fitbit) | Health Sync sends Health Connect to intervals.icu. Lactic walks you through it. |
| Smart scale | Over Bluetooth: Hume Body Pod, Xiaomi Mi scales, Renpho and other QN scales, Etekcity ESF-551, and standard Bluetooth scales (Omron, A&D, Beurer, Sanitas and others). Withings and Garmin Index come in through intervals.icu or Apple Health. Or type your weight in. |
intervals.icu also brings in your ride history from Zwift, Garmin, Wahoo and most other apps, so your fitness is right from day one. Rides and planned workouts sync back.
Bring your own AI (or none)
| Coach mode | What you get |
|---|
| Built-in coach | Chat inside Lactic on a model you pick: OpenRouter, Anthropic, OpenAI, Gemini, any OpenAI-compatible API, or a free model on your computer with Ollama or LM Studio. A morning brief and weekly workout picks with reasons. |
| An AI app you already use | Lactic runs an MCP server on your computer. One click adds it to Claude Desktop; any MCP app can connect. It gets the same tools as the built-in coach. |
| No coach | Just the plan, the workouts and your numbers. Nothing leaves your computer. |
Either coach reads the engine's numbers through tools and suggests changes. You apply or dismiss them. It can also check your gear and connections, and try a reconnect when something's off. Keys live in your OS keychain, never in the screens or the AI.
Cloud models stop at a monthly limit you set (default $10), so there are no surprise bills. Choosing a coach model lists good picks per provider, rough monthly costs and what leaves your computer.
Easy to start
5 minutes and you'll be riding intervals. Five steps: you, your week and goal, your gear, your rides and sleep, your coach. Skip anything you don't have. A short tour shows you around after.
Download
Get the latest version from GitHub Releases.
| Platform | File | First launch |
|---|
| macOS (Apple silicon or Intel) | Lactic_*_universal.dmg | Drag Lactic to Applications and open it (signed and notarized by Apple). |
| Windows | Lactic_*_x64-setup.exe | SmartScreen warns about an unknown publisher: choose More info → Run anyway. |
| Linux | Lactic_*_amd64.AppImage or .deb | chmod +x Lactic_*.AppImage and run it, or sudo apt install ./Lactic_*_amd64.deb. Bluetooth needs BlueZ; keys are stored via the Secret Service (GNOME Keyring or KWallet). |
This is the beginning of the README. Read the rest at the original. Read the full README ↗
