Muscle outlines from Body Muscles by Ivan Vulović, Apache 2.0 — regrouped and recoloured for Muscle Train.
Take a thin resistance band loop and wrap it around any post. Hold the loop, bend your arm at the elbow to 90 degrees and step to the side so the band has slight tension. The band should run roughly along the side of your body. Lower your shoulders and squeeze your shoulder blades together slightly, then smoothly rotate your arm outward: your body stays still, and the rotation happens only at the shoulder joint. Hold the end position for a split second and slowly return your arm to the starting position. Repeat for the required number of reps, then do the same with the other arm.
For proper technique, keep your elbow pressed firmly against your side throughout the movement so your arm makes no extra motion. For better control, you can put a rolled-up shirt or towel under your elbow. Don't try to rotate your arm as far as possible — external rotation can be quite limited at first. Make sure your shoulders don't rise in any position. Don't rush to increase the resistance or switch to thicker bands: the muscles involved are small, and the main goal is to activate them.
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