Physically energy in the kinetic chain is passed by decelerating the prior link. For example in a baseball swing the hips reach their peak speed about two frames before contact and then start to decelerate, the shoulders peak after that but also before contact (Dave Forthenbaugh in his piece “Biomechancs of the baseball swing” cited a max shoulder rotation speed of 766 degrees per second about 57 ms before contact slowing down to 430 degrees per second at contact in elite minor leaguers).

 You want to swing through the ball and not decelerate prematurely but for optimum stability and energy transfer you need to strengthen rotation and anti rotation.

A good way to train that is doing stop swings. For strong adult players I would use a 36-40 ounce bat like in the overload training. Basically is is like a check swing that is a little too late so that the bat stops around perpendicular to the pitch flight in what would be the contact position or better a hair before that. Make sure you stop with bent arms and the back elbow down and front elbow up.

Accelerate as hard as you can and then stop as hard as you can by tightening all torso muscles, back, arms and forearms. The front leg blocks hard and back foot will be pulled forward a couple inches with the torso being slightly leaned back in line with the front leg.

Position should look basically look like that:

http://bloximages.newyork1.vip.townnews.com/stltoday.com/content/tncms/assets/v3/editorial/7/4c/74c33d6d-f42b-53cb-a1ab-e19c5163df0e/518cf5a89c61a.image.jpg

This trains the anti rotation muscles of the torso but also improves forearm strength and teaches to reach a good contact position.

Warning:

Kids need to learn to complete the turn and finish the bat path. Many kids stop their rotation prematurely or never rotate at all and many don’t accelerate through contact. The shoulder rotation does slow down before contact but first it turns full speed until the chest almost faces the pitcher and even then it doesn’t go to zero but continues until the rear shoulder almost points to the pitcher.

So better only do this drill with advanced hitters who already turn well and finish their swings and not with kids who don’t have great intent and a good finish because it could cause them to stop prematurely. Learn to turn hard first and then worry about timing deceleration and optimal funneling of that turn energy into the bat. This is definitely an advanced exercise and great for hitters who pull off the ball and spin through without good direction through contact.

Isometric exercises are an old school exercise to increase strength. isometric contractions are contractions were the muscle can’t shorten because there is a resistance that can’t be overcome.

The drill is pretty simple. find a tree and stand about even with the tree with the front foot. now you approach the tree slowly with the Bat like a slow motion swing and then you push as hard as you can against the tree for 3-4 seconds and you repeat that about 10 times.

Ideally you use a slightly incline tree so that you can push slightly upward like in a swing.

However the word push is a little misleading. You do not want to use the arms but use the turn of the body.

-pull the front shoulder back and up
-hands stay on on the plate side of the body (right for righty)
-hips are extended
-body slightly leaning back to no back arch, keep arch tight)

That drill is for good posture at contact which can lead to better launch angles. losing that posture often leads to lower launch angles.

It also isometrically trains the rotational muscles of the body and also trains forearm strength. Overall it is a good drill that trains all the muscles that fire in a swing and it also reinforces a good contact position.

Physically you are not pushing through contact in a baseball swing but it still is a good drill for better posture and strength.

I believe that the first impulse for the rotation is the back leg drive but soon after that the hips turn on an autopilot and the rear foot usually gets pulled forward as the weight is shifted with the swing. You don’t squish the bug but the back foot releases and slides forward. This is mostly a passive process, the leg is pulled forward by the rear hip.
However I think that one mistake can lead to losing posture and swung plane. You want to maintain that slight tilt over the plate so that you can swing perpendicular to the upper spine ( some tilt the whole spine and some add some side bend so the the lower spine is more upright but the upper spine needs to be tilted).

Now here is the mistake. Many kids bring the back foot around toward the plate with the hip rotation. This causes a balance loss and as a result the player stands up and loses his balance and swing plane.

Here is a demonstration

http://youtu.be/JYdsE6YmNrg
Now the better way is to have the foot pulled forward in a more straight line or actually behind you ( back foot toward shortstop for a right handed batter). This gives you a feel of the rear hip coming forward more in a straight line rather than around ( even though in reality the path still is rotational) and gives some counter balance to the tilt so that you can maintain that posture through the turn.

http://noontimebaseball.com/wp-content/uploads/2014/11/Miggy_fronthigh.gif

It doesn’t have to be that extreme but at least make sure the foot comes forward straight and not to the plate.

For myself I have used the cue slide the back toe to the front heel and it has helped my balance.

It is important to get a drive from the back leg and not lose the back leg load too early (stay back) before you start to rotate. A cue I like to use to maintain pressure on the back foot instep (credit to Justin Stone) until the hips are about a third to halfway open  but then you release all that energy into and against the front side and finish rotation. Don’t squish the bug but drive off the back leg into heel plant and  get all your weight to the inside of the front leg.

Here is the drill ( inspired by Chad Pipitt). You do a swing and try to slide the back foot 5-10 inches forward ( but still stay behind the front side and don’t “stand up”). Then you re plant the back foot and make the next swing. This means you advance a couple inches on each swing, do like 10 swings or cover a certain distance.

This is an easy program for starters. Do it 3 times a week. Note that it only should be done by players with stable mechanics, I would not start before 12-13 years old. Before that work on mechanics and other stuff.

Here is the program. Do it 3 times a week on non conscutive days:

1.extensive warmup

This is extremely important because otherwise you can get injured. Especially make sure to warm up obliques and back, I once strained my oblique doing overload/underload not warming up properly and missed half a season. So REALLY warm up.

2. The tire drill

http://batspeedfitness.com/?p=40

Do 3 sets of 10 swings at full force. Two sets of the strong side and one of the weak side to balance it out.

3. Back step turn drill

3 sets of 6 swings as hard as you can.

http://batspeedfitness.com/?p=59

4. Overload/underload training

2 rounds of 5 swings each with the light, regular and heavy bat ( 30 swings overall)

http://batspeedfitness.com/?p=31

5. Jumps for the legs

a. 2 sets of 8 vertical jumps

b. Two sets of 10 skaters jumps

Another drill for separation ( hips leading the hands) and sequence. Stand with the back facing the target and then take a step back with your right leg ( right handed batter) while simultaneously loading the upper body. Upon landing that leg immediately drives inwards while the bat continue to go back, then you just do a normal swing. Creates great stretch and an effortless swing.

Why should you try to increase batspeed? It is pretty simple: batspeed is the biggest factor for batted ball velocity. Here is a site with some pretty cool calculations:

Click

The formula says that off a Tee the exit velocity is around 1.1 times or a little more the batspeed. That means an 80 mph batspeed with a wood bat would lead to around a 90 mph exit speed off a Tee ( if you hit the ball in the sweet spot of course it can be much less if you don’t hit it on the screws).

Pitch velocity also plays a role but only to a much smaller degree.

Batted ball velocity has a very high correlation with performance. Better hitters tend to have higher batted ball speeds. Home runs in MLB usually are hit at a velocity upward of 100 mph. The hardest hit balls in MLB are around 120 mph, anything above 110 is really smoked.

Click

Batspeed is not everything of course, you also need to make flush contact in the sweet spot and hit the ball in the right trajectory ( home runs usually have a launch angle of around 20-40 degrees). Do increase the chance to make such contact swing quickness and “shortness” ( elite swings take less than 150 milliseconds) is needed as well as a good swing plane, timing and barrell accuracy.

But if you want to become a really good batter increasing swing speed really helps.

This is one of the few drills here that I have created myself. It involves using a car tire slamming it repeatedly into a wall.  Hook the tire with your fingertips ( just the 4 fingers not the thumb). It is important that you only hook it and not grip it to avoid injury.

The good thing is that you already drive the hips open while let the heavy tire is still going back. That way you create a lot of separation, create a good sequence with the hips leading plus using the stretch shortening cycle.

It it is also a great rotational power training because you are overloading in the rotational plane.

I would recommend doing no more than 8 to 10 reps per set so that you can do every rep at max effort.

Here is a video of me doing the drill: