A more experienced climber will have a better understanding of ways to position their body and feet to minimize the use of their arms. This will improve endurance due to the arms's natural tendency to fatigue faster than the trunk and legs. The primary upper extremity muscles used for more technical climbing include wrist extensors and flexors, elbow flexors (including brachioradialis, biceps brachii, and brachialis), posterior deltoid, latissimus dorsi, and scapular stabilizers.
I may be looking at either subacromial impingement or labral tears or both. Check out shoulder injuries of his article. Argh, figure 1 look just like the move I made.