This may be information overload, but for you that would like more technical information on inside/outside mechanics, you might wade through this excerpt from a 2004 post -
Re: last attempt
-- It indicates the direction my analysis of Mark's clips will take.
I have always found it interesting that due to the linear, A to B, hand-path principles that have been taught to coaches for generations, any mechanic that produces a circular motion was believed taboo and would ruin a batter's swing. - If the batter did not swing down at the ball, he was "looping." - If he rotated around a stationary axis, he was "spinning." He must post the front-leg and drive his back-hip forward (back to center). - If the batter's hands did not go straight from A to B, he was "casting." The negative connotations placed on these terms are so ingrained in our thoughts that most coaches still react negatively to them even today.
Ray, I fully agree with your definitions of "To extend." Therefore, our differences appear to be how we use these terms in the context of generating a wide hand-path for outside pitches. You stated, ï¿½The hands had to EXTEND from the one point to the other. You would be correct if the swing had only one axis of rotation (around the spine) - the wider the path of the hands, the more the hands and arms would need to extend.
However, while conducting research of the baseball swing at the U of CA (San Bernardino), we found while using their Motion Study Computer System that there are four main "Axis of Rotation" involved in the swing. --- (Axis 1) the Spine -- Hip- and shoulders rotating around a fairly stationary axis. (Axis 2) The lead-shoulder joint - the biceps area of rotation. (Axis 3) The lead-elbow - forearm rotation. (Axis 4) Point between the wrist. All of these Axis of Rotation produce a series of accelerating arcs. And on the outside of these accelerating arcs is "The Final Arc" the bat-head accelerating around swing plane.
Ray, we found during this study that linear extension mechanics produced a good deal of forearm rotation around Axis 3. This meant the lead-elbow started bent and then straightened out as the hands were thrust outward. Whereas, we found there was little to no rotation around Axis 3 with rotational transfer mechanics. This is because the lead-elbow remains in a fairly fixed position during the swing. In other words, the lead-arm remains fairly straight during the swing regardless of pitch location.
As I just pointed out, the lead-arm does not extend for outside pitches with rotational mechanics. What allows for a wider or a tighter hand-path is the arc position of Axis 2 (lead-shoulder joint). If the lead-shoulder rotates all the way around to the 105 degree position (farthest from the plate), the lead-arm (and hands) will be drawn into a tight hand-path for pitches middle-in. For outside pitches, less shoulder rotation leaves Axis 2 closer to the plate allowing the lead-arm (and hands) to cast out into a wider arc.
In conclusion, I would say the hands do not extend for outside pitches. They are cast into a constant arc around axis 2 regardless of pitch location (except when jammed and the elbow flexes). It is the arc position of Axis 2 that determines how wide the hand-path becomes.