I thought Aroldis Chapman had the fastest pitch on record.
Anyway, I read a study that showed that the shoulder breaks when a certain range of torque is applied. To throw a fastball over 100 mph, it requires torque about that threshold. Or something like that. I may be using the wrong terminology, but the idea is there - throwing that fast eventually ruins the shoulder.
You're absolutely right. This is why pitchers incorporate their whole bodies into a pitch and not just the shoulder. The added momentum is intended to increase torque above the shoulder threshold.