When looking at the evolution baseball over the past several decades, it is amazing to see the progression of power. More players are throwing at high velocity, more homeruns, and of course the homeruns during the steroid era. This may be the time when an understanding formed that being physically developed would lead to greater durability and performance.
For young and developing athletes it can be very helpful in maximizing ability to commit to a training and diet regiment. Making sure the intake and appropriate amount of nutrients needed to fuel the day to day workload is paramount. Recovery and maximizing the workout over a period of time, say a few years, can lead to massive differences in developments. Secondly the training routine will lead to a release a hormonal response that can only be stimulated when put under stress. Sitting on the couch playing video games wont do it.
If you have any questions about how to get going with sort of routine, shoot me an email firstname.lastname@example.org