Fleisig et al. 2011. Risk of serious injury for young baseball pitchers: a 10 year prospective study. Am J Sport Med 39:253-257
The study focused on 481 youths aged between 9 and 14. Injury incidence was simply defined as elbow/shoulder injuries and retirement due to injuries. The study also looked at how throwing more than 100 innings a year, throwing curveballs at age 13, and spending three years at catcher affected injury rates. They found that 5% of young pitchers will suffer a major arm injury within ten years and that this probability increases by 3.5x if the pitcher throws more than 100 innings per year. I could not tell if 100 innings per year is causation or mere correlation. I write this because very good young pitchers tend to pitch a lot into their high school years. In such a situation, they will have more opportunity to be injured. Additionally, the study suggests that young pitchers should not double as catchers.
Fry et al. 2011. Relationships between muscular strength and batting performances in collegiate baseball. J Strength Cond Res 25
Thirty one members of a Division I baseball team volunteered for this study. Muscular strength was measured as grip strength, parallel barbell back squat, and incline bench press, and ball velocity off tee. Performance metrics were batting average and slugging percentage. [If you cannot tell already, I would have completely overhauled this experimental design.] The study concluded that motor coordination is certainly important, but that muscular strength is a factor in batting performance and they suggest all programs need a weight training component. I do not think the study entirely shows that, but it is certainly an idea that would have been ground breaking back in 1975 when it is was thought that flexibility and thin lean muscle was ideal. Nowadays . . . not so much. I included this study to show that not all science being released in ground breaking. A lot of it tries to substantiate common sense.
Kaplan et al. 2011. Comparison of shoulder range of motion, strength, and playing time in uninjured high school baseball pitchers who reside in warm- and cold-weather climates. Am J Sports Med 39:320-328.
In this study, the researchers were trying to determine whether there were physical differences between the shoulders of pitchers in warm weather climates when compared to cold weather climates. The idea being that warm weather pitchers will pitch more and that this increased workload results in destabilizing the shoulder, which is thought to lead to arm injury. 50 pitchers were included from warm weather climates and another 50 were selected from cold weather climates. None of these pitchers had a significant history of injury. Rotational range and strength tests were conducted for each population and then the two groups were compared. Cold weather pitchers had less of a range of motion in comparison to the warm weather pitchers. They also had more external rotation strength. It is generally considered a tighter shoulder (resulting in less range of motion) and a stronger shoulder results in fewer injuries. It was also verified that these issues were related to playing time in a dose dependent manner (this means motion and strength are incrementally affected with time played). This suggests that a healthy pitcher pitches less. However, there is also considerable data suggesting that the number of repetitions correlates to future success. As such, there needs to be a happy medium between being overworked and getting in enough experience. There is probably no bright line criteria for determining what that level is as arms vary in their resiliency.