Hi Jason,
I'm a Dad that was a former Pan American gold medalist in judo when I was
much younger. ; ) I have a 12 yo that really likes to play ball and moreover loves to hit. The one thing I loved the most back in my judo days was to "train". The highest level of ball I played was LL. With all that said, I was on a quest to improve my sons bat speed, so I did tons of research.
I am not big on folklore like "Mickey Mantle used to use a sledgehammer to crush rocks to get stronger/batspeed." Hey if they measured Mickey's mph before and after the training, I would totally be into it. I am sure it helped him, but nothing scientific to back it up, just makes it a nice story imho..
Back in the 70's Eastern block countries (mainly Russia) had huge atheletic budgets(miilions of $$$) targeted specifically at getting atheletes to peak performance wise. Out of this era came plyometrics and overload/underload training. With Over - Under training you use a bat that is light, your game bat and a bat that is heavy. The differences in weight are crucial, how all the bats are balanced is crucial, the amount of reps is crucial. It's all very scientific, but who cares, it works!
Ok, it's getting pretty long winded here. let me say this. My son and I have been using overload/underload training for little over a year now...with excellent results.
You will need a bat speed radar $79 and a specialed overload underload bat designed by (now my good friend) Jon Davis. Here's his website.
Increase Bat Speed Don't try to fake this with bat donuts and a bunch of different bats. Jon has developed exactly what you will need, don't cheap out and suffer the consequences. BTW Jon Davis is a super nice guy and will talk to you on the phone. I was a skeptic at first, so we spoke many times. ; )
The SKLZ over-under set up is a big joke, one size does NOT fit all.
You will need to buy a bat speed radar, then Jon will provide you with a very specialized overload/underload bat and several different work out regimes you can use. (in season - off season etc)
At the end of the day, you are basically taking dry swings with the 3 different weighted bats, 3 times a week. Takes about 20 - 30 minutes to do. You will have verifiable data with the bat speed meter that your bat speed is increasing. Use an excell spread sheet to track you progress. Identify, daily averages, weekley averages, highest mph swings and lowest mph swings. Very exciting stuff!
Make sure your mechanics are good before starting!