Muscle outlines from Body Muscles by Ivan Vulović, Apache 2.0 — regrouped and recoloured for Muscle Train.
Stand with feet shoulder-width apart, knees slightly bent. Hold a dumbbell vertically at chest level, both hands gripping firmly. Engage your core, extend arms straight forward (slight elbow bend), and rotate the dumbbell left, then right, alternating sides.
Engage your core to protect your lower back. Use controlled movements, avoid swinging. Maintain a slight elbow bend to prevent joint strain. Keep shoulders relaxed and breathe steadily, exhaling on rotation.
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