Zone 2 Tracker

Zone 2 training requires maintaining a specific heart rate range for extended periods — typically 60–70% of max heart rate. Most fitness apps focus on high-intensity metrics and don't give Zone 2 the attention it deserves.

Worse, commercial gym treadmills (especially Technogym units) use proprietary Bluetooth protocols instead of the open FTMS standard, making it impossible to get real-time data into a standard fitness app. I built Zone 2 Tracker to solve both problems: a dedicated Zone 2 training companion that works with the equipment I actually use.

The app is built with Expo and React Native for cross-platform support. BLE communication is handled through react-native-ble-plx, which provides low-level access to Bluetooth GATT services and characteristics.

The biggest technical challenge was Technogym's proprietary BLE implementation. Their treadmills advertise custom service UUIDs instead of the standard Fitness Machine Service (FTMS). I had to use a BLE sniffer to reverse-engineer the characteristic payloads, map the byte offsets to meaningful data (speed, incline, heart rate), and build a custom parser.

State management uses Zustand for its simplicity and performance with high-frequency BLE data updates. The architecture cleanly separates the BLE transport layer from the training logic, so adding support for new equipment protocols is straightforward.