I thought that this thread was removed from the forum. I didn't realize that is was moved to this section.
Wow! It is good to see nmgolfer's posts again. I thought that he had disappeared from online golf forums. I especially like his sound argument that the logic of a poster's argumentative position depends on its intrinsic logicality (its intellectual coherence and its concordance with objective reality) and not on the "qualifications" of the poster.
I am not surprised that he found Biomechanic's posts of little value, and I am not surprised that Biomechanic thought he was a Jeff-clone.
Going back to the "facts" regarding the kinetic chain - I agree with nmgolfer that the kinetic chain and COAM doesn't apply to torso movements in a golf swing. However, I think that nmgolfer is wrong about two points.
1)I think that COAM does apply to the relationship between the movement of the left arm and the clubshaft.
2) I think that the the left arm slows down prior to impact.
nmgolfer only quoted one source that claims that the arms/hands do not slow down prior to impact - Nesbit's research study. However, there is substantial evidence from many other sources that demonstrate that the left arm/hands do slow down prior to impact.
An explanation of why the hands should be expected to slow down prior to impact comes from an understanding of TGM mechanics. Here is my personal explanation.
In a pivot-driven swinger's action, the pivot supplies swing power that is responsible for the release of PA#4. From then on, the body pivot motion does not affect power production because the PA release sequence is 4:2:3 and PA#2/3 are passive release phenomena. The club is an inert object that doesn't know from where the source of power is derived - it only responds to the pull force at the grip (exerted by the left hand). In that sense, the double pendulum swing model applies. The clubshaft is equivalent to the peripheral arm and only responds to pull forces exerted at the peripheral hinge joint (left hand), and the peripheral hinge joint only moves as fast as the central arm (equivalent to the golfer's left arm).
In a pivot-driven swing, the pivot supplies swing power that causes the release of PA#4. Once PA#4 has been released, then no more energy is imparted to the system of the flying left arm (from the central torque generator = body pivot motion) . In that sense the flying left arm is a motional system containing a "fixed" amount of energy. When PA#2 releases, and the clubshaft becomes more in line with the left arm, then the left arm must slow down. There are two valid explanations for this phenomenon. The one explanation relates to COAM.
Explanation number 1
If the left arm (central arm)/clubshaft (peripheral arm) is a system in motion, and there is a "fixed" amount of energy in the entire motional system, then the central arm must slow down if the peripheral arm speeds up - because energy moves from the center to the periphery.
Explanation number 2
Another way of understanding this COAM phenomenon relates to the distribution of the COG relative to the axis of rotation. If the COG of the entire motional system moves further from the central axis of rotation (which is the central hinge point from which the central arm is suspended in a double pendulum model), then the entire motional system must slow down. That's the explanation evoked by David Tutelman in his explanation.
I now believe that the hands slow down prior to impact (because the left arm slows down prior to impact) in an excellent golfer's swing and it's a good thing - because it allows time for release of PA#3 and the squaring-up of the clubface prior to impact.
Here is a capture image of Tiger Woods swing - videod at 4,000 frames/second. Every white dot joining those red lines represents 10 frames (1/400th second) and one can see that Tiger's left arm slows down just before impact.
There is one other unquantifiable factor that makes my COAM explanation far from full-proof.
The COAM idea is based on the belief that all the energy propelling the clubshaft is only passively derived from the left arm (according to the principle of COAM), and that the left arm derives all its energy via the release of PA#4. However, one needs to consider another factor - the role of left forearm muscles in actively releasing PA#2 and/or PA#3. If the left forearm muscles supply any energy to actively release PA#2 or PA#3, then the left arm may not need to slow down as much as predicted by the COAM theory.
Hybrid Mode
