Muscle outlines from Body Muscles by Ivan Vulović, Apache 2.0 — regrouped and recoloured for Muscle Train.
Lie on your back, knees bent, feet flat. Hold a dumbbell in each hand, palms facing each other, arms extended above your chest. Lower the dumbbells out to the sides in a wide arc until your upper arms touch the floor. Pause, then return to the starting position. Repeat.
Maintain a slight bend in your elbows. Engage your chest muscles, control the movement, and use a slow, deliberate pace. Avoid bouncing the dumbbells off the floor. Exhale on the lift, inhale on the lower.
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