Posted by: Jack Mankin (MrBatspeed@aol.com) on Thu Mar 1 12:41:41 2007

>>> Hi Jack

Jack you are over simplisizing the mechanic behind the x factor stretch. The hips maximum rotational velocity is before the shoulders maximum rotational velocity and the hips rotational velocity is decreasing while the shoulders are increasing. Video can not measure rotational velocities only by a system like that on Skills Technology or simular computer monitered device can you accurately measure this.

Take note that the hips rotate at a slower rate then the shoulders so in your video the hips would have to lead the shoulders if they are to be open near the same time. Therefore the further the hips can rotate before allowing the shoulders to rotate the faster the shoulders must rotate in order to catch up. I believe this is what you call linkage. To put it another way the hips must begin to decelerate before the shoulders hit maximum rotational speed or the combination of the two body parts would cause the hitter to 'spin out' or overrotate as there is no portion of the body that can help declerate the bat. This is a key factor in the casting of the hands but that is another discussion.

Jack if you download the skill technologies program you can look at the graphs of rotational speeds and x factor stretch. They can be very enlightening.

I found a quote in a book the other day about Hank Aaron. In the quote a reporter was talking about the fact that the coaches of Hank's team where flappergasted at the fact that in photos of Aaron's swing his back foot was off the ground when he made contact with the ball (not bug squishing). Yet 50 years later when the Detroit Tigers make it to the World seires and you see the video of the same thing it was a new concept.

New technology opens the eyes to more percise analysis of the same motions and if we open our minds to what our eyes see we will learn more then we knew before.

Dave P <<<

Hi Dave

I am not just relying on video for my analysis. At the U of CA (SB), we used a Motion Analysis computer that gave angular displacements rates for the 14 sensors we placed on the bat, arm, leg and torso joints during the swing.

Note: By “unison,” I am not saying they rotate in lock-step. Obviously, with the addition of torso muscle contraction to hip rotation, the shoulders rotate at a higher rate.

Jack Mankin