I wrote a story on the increasing amount of arm injuries in baseball a year or two ago, and this was the prevailing theory from orthopedics:
The growing epidemic of ligament and tendon damage in athletics today is partially due to the superior conditioning of today's athletes. They push themselves to physical limits that athletes in past generations just didn't reach, and their bodies simply can't keep up.
Increasing muscle mass puts stress on ligaments and tendons. That's obvious. But with the growth of the high-intensity circuit training that emphasizes quickness, the bigger muscles are moving faster, making athletes move faster, and it creates a perfect storm for ligament damage.
Athletes are supernatural, in a way. Their bodies aren't built to withstand the pressure and intensity that athletes put them through.