I'm an avid sports fan, especially of baseball. I noticed one day how far back the pitchers move their arms when pitching. I tried to put my arm in that position and couldn't come close. How do they do that?
Just as you noticed, overhead throwing athletes move the throwing arm through a wide range of motion over and over and over. And they do that everyday whether in practice or in competition and sometimes both on the same day. Like most things in sports activities, practice makes perfect. Their training goes year-round now and includes stretching and flexibility exercises along with strengthening and endurance training. Using the throwing action 100s and 1000s of time eventually stretches some of the soft tissues around the shoulder while strengthening others. In fact, most pitchers don't really have more motion than you do. It's just the location of that motion that changes. The normal range-of-motion in degrees for shoulder rotation (full external rotation to full internal rotation) is about 180 degrees. The throwing athlete, especially baseball pitchers, can be anywhere from 160 to 180 degrees. They end up with more external rotation of the shoulder joint (pulling the arm way back to throw the pitch) but sometimes less internal rotation. As you might imagine the excessive motion or extreme range-of-motion that comes with repetitive throwing motions can also result in microtrauma of the soft tissues in and around the shoulder. This type of physical action tests the tensile and physiologic limits of the shoulder structures. Injuries such as tears of the labrum/i> (rim of fibrous cartilage around the shoulder socket), impingement (pinching of soft tissues inside the joint), and tendinitis are common in pitchers.