You didn’t mention the ages of your athletes. There are some differences between young (nine to 19 year olds) versus older (college aged) athletes. One thing that’s the same between the two groups is the increased number of ulnar collateral ligament (UCL) injuries.
UCL injuries are clearly on the rise. The number of high school pitchers needing UCL reconstruction each year has tripled over the last 10 years. Overuse of the throwing arm and throwing breaking pitches too early may be linked with this problem.
Results of studies comparing volume and type of pitches report that quantity makes a big difference. Type of pitches seems to be more variable in the effect on injuries. Some studies show significant differences between pitchers using breaking pitches and those who don’t. And age when breaking pitches begin may be important but hasn’t been proven yet.
The evidence seems to point to quantity of pitching as the most important risk factor. Arm pain and arm surgeries among young pitchers occur more often based on the total number of pitches delivered over time rather than the type of pitches.
Type of pitches does have its importance. Elbow and shoulder are loaded most with fastball first, then curve ball pitches. Change-up pitches don’t have nearly the same impact as these other two types.
There’s a lot to be said for a good training program that builds up overall strength and endurance for each athlete. Balancing pitching schedules throughout the year is important. This is especially true in those geographic areas where the game is played year-round without a significant break.