Set-up: Stand sideways to a cable tower with the cable set to roughly hip height. Drop your upper arm in line with your upper body and your elbow flexed at 90 degrees. Stand with a tight core, a slight bend in the knees and a neutral back.
Lift: Keeping your elbow fixed on your side, start the movement with your forearm in front of your body. Rotate your forearm away from your body, keeping the 90 degree angle at your elbow. Return the cable to the start position slowly with control.
Emphasis: Do not use momentum. Keep motion in the rest of the body to a minimum. Do not shrug the movement to involve the traps or let the shoulder move forward to engage the deltoids. Any of these deviations will reduce the load on the external rotators.
Repetitions: Perform all prescribed reps on one side, then on the other. This counts as one set.
Muscle Roles in external rotations - standing, cable