1. The app could use photogrammetry and mesurements like waist, length, neck and so on to create a realistic 3D visualisation of your body.
2. With the use of sliders you can customise your 3D body to reflect your goal. So back slider, wider back, like Autodesk character creator https://charactergenerator.autodesk.com/
3. Once you adjust all the sliders to the look you want, the app will create a work out program and macronutrient intake ratio plan to achieve the 3D desired results in say 10 weeks.
4. And it would integrate with garmin connect to send and recieve workouts to the watch .