Muscle outlines from Body Muscles by Ivan Vulović, Apache 2.0 — regrouped and recoloured for Muscle Train.
Lie face down; elbows 90°, upper arms at shoulder height, forearms forward/hands by ears (W-shape). Brace core/glutes; forehead to mat, shoulders down (no shrug). Lift forearms: drive elbows back, externally rotate shoulders, retract scapula ("blades to pockets"); upper arms stay level. Top: squeeze blades 1-2 sec (feel mid-back). Lower controlled (2-3 sec). Repeat.
No shrug: shoulders down to pockets (targets rhomboids/rear delts; reduce ROM if traps dominate). Hold W-shape: upper arms perpendicular/sideways, forearms forward (not rowing). Externally rotate: thumbs to ceiling, palms forward/up at top (hits rotator cuff).
MuscleTrain is actively being built. If something looks broken, or you have a suggestion, let us know — it really helps shape the app.