Posted by: Graylon (g_dunc@hotmail.com) on Wed Aug 20 17:12:13 2008

> >>> Thanks for the video. We see things slightly different. IMO the forwrd "linear" momentum is stopped, especially when you stop the video at foot plant. The forward momentum is not gone it continues in the rear hip. I do agree that the axis of rotation IS NOT the front leg, but rather the rear hip.
>
> I'll use foot plant in this video as my point of reference as you did. The rear hip is loaded it is pulled in or back towards the first base dugout and the lead hip is starting to ever so slightly open. As the frames advance you see the lead hip open more, as the rear hip starts to unload, driving forward to replace the front hip. The lead leg continues to straighten driving the lead hip back and out of the way.
>
> Why I don't believe the base of the spine is the axis of rotation. If this was the case then the rear hip would have to go out towards the plate and then around the spine, like a revolving door, I do not see this. What I do see is the lead hip clearing the way and the rear hip driving more "linear" in the direction of contact. Of course it will be "rotational" because the front leg as blocked any forward slide of the hips and weight shift. Therefore, I have come to the conclusion that the rear hip is the "pivot" point of the bodies rotation. The spine does not stay stationary, like a rod stuck in the ground, but it will actually move out of the way also.<<<
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> Hi Graylon
>
> Just to clarify a few points for our discussion. (1) Do you agree that the head and neck should remain still during rotation? (2) If you agree, then would not the shoulders be rotating under the head like a revolving door? (3) If you agree, this means the shoulders rotate about the top of the spine - like a revolving door. What mechanical advantage do you find in the hips having a different axis of rotation than the shoulders – the spine?
>
> Jack Mankin


Jack,

I don't have much time. I need to get to practice, so I will try for short answers. I will try to elaborate later if need be.

Question #1 Yes Question #2 No

Question # 3 No, If the shoulders where to act like a revolving door they would just be turning, the lead shoulder would be going away from the plate and the rear shoulder towards the plate. This would be the only way they can get around the spine. IMO this would be to slow. The lead shoulder goes up as the rear shoulder comes down (lateral tilt). The hips ultimately win with the rear hip "grabbing" the rear shoulder sending it forward. The shoulders do rotate but they try to rotate more like a ferris wheel rather then a revolving door. They obviously can't rotate all the way around like a ferris wheel but they need to in order to lock up with the hips. I guess I would say that the shoulders somewhat rotate like the hips, with the lead shoulder being pushed out of the way.

Question #4
Short answer using the rear hip as a "pivot" point allows for the greatest adjustability. I can pivot off of the rear hip in any direction. If I use the spine as the "axis" of rotation then I have only one way to go and that is to spin. Not a lot of room for adjustability. Using the rear hip also allows me to create momentum with out weight shift. using the spine I must first weight the front foot then swing. IMO again no room for adjustability and I will again spin.

Graylon

Graylon