Lessons from Building Motus, an iPhone Fitness App That Tracks Reps via Camera

Motus is an iOS fitness app developed by LoudOwls that uses the smartphone camera to automatically track body movement and count exercise repetitions, removing the need for manual logging. The app was built natively with Swift and SwiftUI, using GuruSDK for camera-based body tracking and Supabase for user accounts and social data. Rather than functioning as a standalone feature, the camera tracking is embedded within a structured workout flow that includes exercises, sets, rest periods, and rep targets. A key design challenge was ensuring the tracking worked reliably during real movement while keeping the user interface minimal, since exercisers rarely have hands free to interact with their phones. Motus also incorporates social features such as a feed, stories, and reactions, reflecting the insight that technology can capture workout data while community engagement drives long-term user retention.