>>> Can you possibly elaborate a little more on this subject, especially regarding the "motion study computer" and the data you collected? I read this posting recently and had it in mind as I watched my son's game today. I think a light bulb went off! Although I think I have a pretty good understanding of rotational swing mechanics and the applicable laws of physics, I had never really given much thought to just how detrimental even a slight extension to contact could be to batspeed and power. I appreciate that more now with the realization that "extension to contact" destroys both CHP and Torque, the two critical components to batspeed. And if a hitter extends to contact, the extension occurs after the hitter has overcome inertia, built some velocity in the swing, and just as he should be shifting into overdrive. (front shoulder pulling back to catcher 105 degrees) Instead, the extension is like taking your foot off of the throttle and coasting to the finish line (point of contact). Hence the power curve peaks before contact and never reaches its full potential.
Perhaps you could provide a side by side analysis of a professional hitter and a young hitter, showing their respective batspeeds and hand speeds at various points in their swings from start to finish and especially, relative to the point of contact. <<<
In the mid 1990s, we conducted a study of how energy is transferred in the baseball swing at the U of CA (San Bernardino). We used their newly acquired Motion Study computer with 4 position motion detectors, pressure sensors and high-speed cameras. Sensor points (looked like miniature Ping-Pong balls) were placed at each joint of the batter's body and at the knob and end of the bat,
The linear velocity and angular displacement rate for any limb (or joint) at any point of the swing could be analyzed. As far as it pertains to this discussion (BHT), the data supported video analysis conclusions -- 'Approaching contact, the greater the rearward trajectory of the lead-forearm, the greater the bat speed generated.'
Below are video clips from Batspeed.com Archives that should address your question and request.
The last clip, "4 Good hitters -- Back Arm," show their back-arm still back in the "L" position at contact. The "L" position allows for more balance between 'back-side-drive' to 'lead-side-pull.' --Back-side dominate hitters tend to have the back-arm extended which greatly reduces 'lead-side-pull.'
Bonds and Burrell Applying BHT
BHT - Good and Poor
4 Good hitters -- Back Arm
Note: Since this is an important topic for generating bat speed, I am featuring it as a new thread.