Side-Lying Dumbbell External Rotation

You let the elbow float away from the ribs, which turns a rotation into a lateral raise.

You roll the shoulder forward at the bottom of each rep to gain range.

You go heavy and start jerking the dumbbell up with the body instead of rotating smoothly.

You stop well short of the top position and never reach the range that matters most.

Pin the elbow to the ribs like it is bolted there and let the forearm be a hinge around it.

Rotate up slowly as far as it comfortably goes, pause, and lower even more slowly across the belly.

Choose a light dumbbell and count the tempo; this is a control drill, not a strength lift.