Posted by: tom.guerry (eights) on Sun Oct 28 09:02:47 2007

Jack-

I remember that you have done motionanalysis as well that you said was similar to Zig's findings which are summarized by his posts here in 2002-3.

These finding should help guide interpretation of video.

I think Zig's motionanaysis with markers on front hip,front shoulder,lead hand and bathead give a reasonable average range for mlb swings of amount of hip to shoulder separation (x-factor) and rate of separation (x-factor-x-factor stretch) and how this
relates to expected/optimal progressive "speed gains" (kinetic link/segmentation/summation of velocity) of each segment or as you call it "arc", and how these vary with in (low load) vs out (high load situations.

Applying this to what is generally seen in video, I think this requires,among other things:

Inward turn of whole body which does not involve much oil/separation (perhaps a tiny bit depending on how you hold bat and what sequence you move the body parts in and inertia) but must turn the entire body back to allow room later for deep contact with early batspeed for some locations and which involves tilting/loading the front shoulder down and in and which begins the back and forth negative and positive move of the hips and weight distribution.

Hip and hand cock which prepares the upper and lower body for coiling and control of weight shift.

Then comes "prelaunch THT" or "rotation into toe touch" where active coiling starts by keeping hands and shoulders back as front leg then hips open. This creates an average of 15 degrees of separation/coil, weight still going forward and down, front shoulder still tilted down and in. Pitch location is beginning to be recognized and individual swing timing and plane matching adjustment started beginning to determine degree of "sit" and range of swing radius and positioning of shoulders preparing for tilt and direction of
weight shift. Handle torque starts bat back toward catcher, front leg then hips start to open, shoulders/hands stay back while coil is produced.

ZIG -

"In this loading phase, which many of you call a backwards weight shift, the best athletes have a slight change in the position of the hips and shoulders, closing to a position of approximately 25 degrees of the hips and 40 degrees of the shoulders {X-Factor is now
approximately 15} (This is accurate to 1mm)"


Then comes "THT at initiation/launch" which produces an additional almost 15 degrees of torso stretch/separation with a last quick stretch (x-factor stretch) which enables effective/controllable (well timed and directed) reversal/unloading. Hands fire bathead by
handle torque, forearms swivel (no bind becasue of good grip and arm/forearm sequncing/position), shoulders tilt, hips urn/accelerate to max angular velocity. Upper body resists/stays back. This permits quick acceleration and acceleration that starts well back/early in the swing plane. Swing plane and CHP/timing is set at end of this phase which is finished just prior to the "lag position".

ZIG-

"As force is applied to the back foot, it creates a linear shift of weight, at the same time, their is a release of rotational energy around (rotating) from the front foot up to the hip of the front leg (the heal of which has dropped during the linear/rotational shift, to provide a solid front side to hit against). At this point there is an X-factor stretch of approximately 12 degrees (x-factor stretch is an increase in the degree of separation between the hips and shoulders)."


Then comes the swing from launch of bathead outside of arc of handpath to contact. Hips decelerate and torso accelerates the now conncted upper body/shoulders/hands/bat at which point the swing resembles more closely the modified double (or multiple) pendulum
type "ironnyman" model (still with additonal biomechanical elasticity and force production unaccounted for by the purely mechanical model).

The CHP and handle torque blend optimally to produce expected "speed gains"/summation of velocity of each link. The better you do this, the more consistent and dependable and repeatable your swing timing and plane matching and most importantly, the lower your timing error as spatial error remains acceptable.

ZIG-

"During this first phase of the swing the forward swing there is an expected angular speed gain (progressive speed gain) of pproximately 200 degrees per second from the hips to the upper torso, as the hips rotate and peak to a speed of 550 d/sec [during "initiation" which ends at about the "lag position"], and upper torso rotates and peaks milliseconds later at a speed of 750 d/sec. There is an additional speed gain of approximately 250 d/sec from the upper torso to the arms (which reach a speed of 1000 d/sec milliseconds after the upper torso). This is followed by a significantly higher gain of 1000 d/sec from the arms to the bat as the bat releases at a speed of over 2000 degrees per second. Good athlete = 550>750>1000=2000 degrees per second (rotational bat speed)."

During the approach to contact from bathead launch the torso/front shoulder decelerates such that it keeps turning right up to contact as you have noted. Outside/high load involves more handle torque and a longer swing radius.

Inside/low load involves more turn and less handle torque.

ZIG-

middle location:

"With respect to the acceleration and deceleration in the forward swing, as the player swings the bat the hips slightly lead the sequence, followed immediately by the combined acceleration of the shoulders, arms or hands, and the bat. The hips reach maximum
acceleration between 510 and 585 degrees per second of rotation, followed by the shoulders (upper torso) 700 to 900 degrees per second, followed by the hands/arms, 900 to 1150 degrees per second, followed by the bat release speed of between 1750 to 2300 degrees per second. Done effeciently, the hips reach maximum rotation [not acceleration, but most open position] (on a middle plate pitch) when the bat is perpendicular to the straight line from the pitcher. This means at hip rotation of 70 to 85 degrees of rotaton, the shoulders at this point rotate to approximately 65 to 80 degrees or rotation."

NOTE: contact needs to be made BEFORE the shoulders entirely catch up to the hips or there will have been DECELERATION before contact. The point at which there is still acceleration as evidenced by making contact with hips still somewhat ahead of shoulders is called "near locking".

Outside vs inside location:

ZIG-

On an inside pitch, this "near locking" of the upper torso and hips occurs with the hips at 92 to 100 degrees. On an [out]side pitch, this can occur as early as 65 to 72 degrees. The shoulders should lag by approximately 5 degrees on an inside pitch and 10 degrees on an outside pitch. This amounts to less than an inch of seperation, but can be the difference between a pop up/weak grounder and a hard hit line drive."

In any case, batspeed max is ideally at contact.