If you've ever felt a twinge—or worse—in your shoulder during a military press, you're perfectly aware just how important and fragile your rotator cuff is. But you might not know the rotator cuff is made up of four different muscles. The two external rotator muscles, teres minor and infraspinatus, are especially important.“They stabilize the head of the humerus (upper arm bone) in the socket of your shoulder blade during overhead movements, create external rotation of your upper arm, and play an important role in keeping your shoulder stable,” explains strength coach Pete McCall, M.S., C.S.C.S. “If you're seated working on a computer all day, your shoulder is internally rotated. But these muscles help fight that internal rotation so your shoulder can move impingement-free.”To keep these small-but-mighty muscles strong and able to do their job, McCall recommends strengthening the entire rotator cuff—including the internal rotators, supraspinatus and subscapularis muscles—together. “This enhances their function and stability,” he says. Do these as part of your warmup before a shoulder or chest workout. 3 exercises to strengthen your teres minor and infraspinatus 1. Shoulder diagonal raiseThis controlled movement uses a light load in a wide range of motion. Hold a single dumbbell in one hand, just in front of your pelvis. With control, raise the weight up and on a diagonal away from your body, finishing with your hand extended straight out (imagine the letter 'T' cut in half). You want your arm away from your body, parallel to the ground, and your thumb up. Lower down. Do 10 to 12 reps on each arm, going for 2 to 3 sets. 2. High plankThe isometric nature of the high plank makes your shoulder rotator muscles do their job in the most functional way. Place your hands on the ground, and kickstand one foot up onto the toe, then the other. “Press your hands into the ground and your arms back into the shoulder blades,” says McCall. Hold for 30 to 45 seconds. Rest 30 seconds. Repeat 2 to 3 times. Bonus: Your core muscles get a boost as well.3. Plank rotationA progression from the straight-arm plank, the plank rotation challenges your rotators further by adding movement. Start in a high plank. Squeezing your hips, rotate to a side plank, balancing on one arm and the side of your foot closest to the ground. With control, come back to the high plank by replacing your free hand to the floor. Now rotate to the opposite side. That's one rep. Do 6 to 8 reps. Rest for 45 seconds. Complete 2 or 3 sets.