From Eric J. Hörst at NICROS (All of them)
External Rotation. This simple exercise, done with a 2.5 or 4.5kg (5 or 10 lb) dumbbell, will help strengthen your rotator cuff...and perhaps make you more bullet-proof on shoulder-wrenching climbing moves.
While climbing provides a rigorous workout for the pull muscles, it demands much less of the antagonist push muscles of the chest, shoulders, and upper arms. In the long term this could lead to tendinitis or other injuries, as these stabilizing push muscles may fall out of balance with their opposing pull muscles. The two most common problem spots are the elbows and shoulders. Let’s take a quick look at each.
First, consider how climbing ceaselessly works the finger-flexor muscles of the forearms, yet does little to strengthen the extensor muscles on the outside of your forearms. As a result, climbers tend to develop a significant muscular imbalance and a susceptibility to lateral epicondylitis—a painful tendinitis on the outside portion of the elbow (also known as tennis elbow). As many as one in four climbers will eventually suffer from this affliction, although you can greatly reduce your chances by performing a simple preventive exercise. Reverse wrist curls with a light dumbbell will strengthen the extensor muscles on the back of the forearm. Perform this exercise, along with stretching of the forearm muscles (also do on rest days), before and after every climbing workout; chances are you’ll dodge the elbow tendinitis bullet.
The shoulders are another common site of injury, especially among climbers with a preference for overhanging walls and steep, severe boulder problems. Climbs of this nature place great leverage and strain on the shoulder joint, and it’s the push muscles of the chest and shoulder, and the smaller rotator cuff muscles, that help maintain stability. Of course, climbing does a poor job at strengthening these vital muscles. The upshot, for some unfortunate climbers, is that shoulder instability can lead to tendinitis, subluxation (partial or complete dislocation), and rotor cuff injury. Again, the use of a few basic push-muscle exercises will help maintain balance and, hopefully, keep you injury-free. Push-ups, dips, and dumbbell shoulder presses are three exercises I advocate for this purpose. Two or three sets each, twice per week, is usually enough to keep the push muscles in condition to do their job. (Should you possess an existing shoulder injury, however, please consult a physical therapist for more appropriate rehabilitation exercises.) Most important: train the smaller rotator cuff muscles with a light dumbbell or exercise band, by doing one or two sets of 20 to 25 repetitions.