Posted by: tom.guerry (eights) on Sat May 3 12:03:37 2008

I think the generic mechanical golf swing model works for the baseball swing as well, see Physics of golf, Jorgensen, illustrated here :

http://www.tutelman.com/golf/design/swing1.php?ref=

Jack's baseball swing model covers the handle torque and the CHP/connection to body ("transfer mechanics") the best.

The twisting and untwisting of the body/torso is well explained as the well known (studied in many sports/skills) kinetic link/chain, including the xfactor and "xfactor stretch" ("cusp") descriptions from golf.

How exactly the forward motion of the whole body works remains somewhat of a mystery (at least to me). One principle/"absolute" that is proposed in golf probably works for hitting as well which is that you must avoid "reverse pivoting" which means that the center of gravity of the body needs to flow forward/not fall back before contact.

Beyond that, forward motion of the body depends on if/how you think adjustments are made for the pitch as location is recognized.

I think the best description of how the body works to adjust up/down is from Epstein, following Williams. This is the concept of "lateral tilt" of the shoulders. This is the same way the shoulders work in the "classic" 2 plane golf swing.

Tilting of the scaps (shoulders) is synched with "shifting" of the weight. The combination here of shoulder tilt resisting turning open as well as forward shift of the base of the spine sets torso/spine angle on the fly and fine tuning is done to create a matching impact zone by how much the lead arm is lifted as it connects through the lead scap to the torso.

This shoulder resistance finishes twisting/loading the torso with a quick well directed "stretch" ("cusp"/"x-factor stretch") which unloads with quick well timed and directed acceleration of the bathead to optimize the "impact zone".

The "resistance" to turning comes from the torquing of the handle of the bat which starts rearward acceleration with arm and forearm action, then further resistance and adjustment as location is better recognized by aditional acceleration as the shoulders tilt.

This late tilt adjustment requires early swing preparation so that forward motion of the whole body is underway, AND stretch/twist ("x-factor") of the torso is underway and not prematurely interrupted.

This early forward momentum of the body is what is primarily "metered" or controlled by hinge of the back knee.

I see all high level bb swings adhering to the same overall sequence:

1 - rhythmic preaswing activity (preparing for the separate/torquing action of the handle via the hands, hands NOT used as in golf as more of a single action hinge).

2 - inward/backward turn of the whole body which involves cocking of the hips as the weight goes to the back foot when the front foot is lifted and front knee turned in

3 - forward momentum of the whole body as tha hands "cock"/lifting of back elbow

4 - "rubberbandwinding" (active twist/load of torso begins) as the hands and shoulder stay back while the front leg then hips open and the center of gravity lowers with "sitting" posture change to keep muscles on stretch.

5 - drop and tilt - the synched shoulder tilt/weight shift

6 - swing


The forward momentum of the whole body as the hands cock is produced primarily by spreading (aBducting) of the legs using the back foot as a base. Back leg "hinge" means flexing of the back leg to slow down this forward momentum with location recognition to adjust for offspeed or to stop forward progress of the body to keep the spine angle/axis more leaned back to then create an "impact zone" that matches the low or dropping type ball trajectory.

This back leg hinging seems to me (after Epstein) to be primarily controlled by the action of the back shoulder/scap. The back leg flexes at the knee or "hinges" when the back scap is lowered. If you keep the back shoulder up, the weight continues to flow forward to assist in getting the body upright to match a high heater. Dropping of the back shoulder keeps the weight/axis leaned back.

In any case, when you make the "GO" decision, you have to tilt the shoulders together (front up, back down) synched to shifting of weight (base of spine) forward. If weight has already gotten to front foot, this does not work, which is how you get caught on the front foot. "Sitting longer" by hinging/flexing back knee is required in cases like this to delay the forward momentum of the body.

Once the weight "shifts" at "GO", then the weight has to continue to flow to the front foot with center not falling back before contact (or there will be bathead deceleration/"disconnection" before contact which raises timing error and makes collision with ball inefficient). In golf this is described as part of avoiding "reverse pivot".

Top hand action has much more to do with in/out/swing radius adjustment as Jack has detailed well. This allows you to hit these balls with authority. If you work too hard on poorly understood concepts like "trying to avoid casting" or "maintainging the hinge angle" in the wrists, you will inhibit the "THT" ("immediate launch and spend") necessary to make good swings. Another important aspect of "early batspeed".

Where Jack and I disagree somewhat is in the details of the shoulder action. I think it is necessary to emphasize shoulder TILT which results in "keeping the front shoulder in there".

Jack's argument against this is that this will usually result in inhibiting shoulder TURN, and shoulders must turn well from launch to contact for a qucik swing with early batspeed and no premature deceleration.

My thinking, however, is that the shoulders must be used to tilt as a method of twisting/finishing torso load better (then hands stay back more and bathead accelerates more quickly with better timing and plane matching) and this better twisted torso is what keeps the connected shoulders turning well all the way to contact.

My experince is that if you instead emphasize TURNING the shoulders at "launch", you end up with a less effective and less controllable twist/load of the torso and lose optimal early batspeed and well matched impact zone.

The shoulders tilt/resist while the hips shift and turn with the hip turn working itself up to turn the connected/resisting shoulders. Active turning of the upper torso or shoulders dampens the end of loading and interferes with the sharp unlading necessary for effective acceleration of the bathead.

Relative to this active/"turn shoulders like heck" feel, the shoulders have more of a tilt/"bypass" feel with emphasis instead on the synched forearms torquing the handle (assisted by shoulder TILT) as the hips shift and turn ("drop and tilt") producing a better/quicker result.

To briefly address the top hand feel, it controls the timing and direction of handle torque which controls setting of swing trajectory and which is necessary to avoid bathead "drag", moreso for outside and low pitches, otherwise hitters swings fall behind the power curve as the swing radius (and resistance to rotation) increases.

Jack has excellent descriptions of this, which is a necessary component of "early batspeed".


Jack's is the only model adequate for explaining these essential in/out adjustment and early batspeed concepts which are crucial for high level hitting.