The rotator cuff warm-up is a simple exercise targeting the rotator cuffs through weighted shoulder external rotation. It's a classic way to warm up the shoulder prior to sports or training, as well as a common rehab movement. The rotator cuffs are a notorious injury-prone structure in the shoulders of Major League pitchers and other athletes. This is a movement most commonly done for moderate to high reps, such as 8-12 reps or more per set.