Muscle outlines from Body Muscles by Ivan Vulović, Apache 2.0 — regrouped and recoloured for Muscle Train.
Start on all fours with your arms fully extended and elbows locked. Protract and depress your shoulders, engage your chest, shoulders, and core, then lean forward until your weight is over your hands. Lift your feet off the floor while keeping your hips slightly open and your body under full tension throughout the hold.
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