Muscle outlines from Body Muscles by Ivan Vulović, Apache 2.0 — regrouped and recoloured for Muscle Train.
Stand with feet shoulder-width apart, holding a dumbbell. Extend arm overhead, palm forward. Slowly lower the dumbbell behind your head, bending your elbow. Pause at the stretch, then extend back to the starting position, contracting your triceps. Alternate arms.
Maintain a neutral spine and engaged core. Keep your elbow close to your head. Control the movement, avoid momentum. Start with a lighter weight. Exhale on extension, inhale on lowering.
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