Your arm is not the only body part involved in throwing a ball- the whole body is involved! Proper strengthening, stretching, and mobility are important for the whole body. What makes it hard to simply give a preseason routine to a group of athletes to follow is because every person has strengths and weaknesses are all unique to each individual. A general routine will not do in addressing these individual needs. A screening may be necessary to specifically see what individuals need to work on. Some might need mobility, others strength, and most both.
A great tool to determine what an athlete needs is a Functional Movement Screening (FMS). FMS is a test that a professional can administer to see areas that can be improved. Mobility is of the utmost importance, followed by stability, and then strength. Moving to quickly to strengthen without having the mobility and stability often leads to injuries. If you are not sure of your mobility, have a professional from Peak Performance put you through the Functional Movement Screen to find out what you can improve.
References
Gray Cook (FMS)
Arnold Tobin Specializing in grip strength
Hector Duprey, Baseball specialist
By Corynne Pereira