[Jeff]

Biomechanic - seeing that you are new to this forum, perhaps you should notify the forum members here that you work for a company that is competing with TPI. That will allow them to evaluate your comments with special care.

There are two approaches to this issue. The first issue is what represents the correct measurement data and the second issue relates to the issue of biomechanical plausibility.

I will first deal with the issue of the correct measurement of angular velocity.

The TPI researchers describe their methodology in this pdf paper and they contrast it with the technology used by Zenolink.

http://perfectgolfswingreview.net/KinLinkvsKinSeq.pdf

If one reads the paper, one can see that the TPI researchers use a totally different methodology of measuring angular velocity in the sense that they do not relate it to the PTS plane, which is apparently a requirement of Welch's zenolink technique. It would be interesting to see both measurement techniques used on the same golfer to see whether the graphs produced by the two different systems are radically different.

I find the Zenolink's results problematic for a number of reasons.

Here is a link to a golf instructor who is using the Zenolink system, and you can see the type of graph produced by Zenolink.

http://www.biosporttechnologies.com/html/biomechanics_golf_swing_kinetic_link.htm?action=bi omechanics_gskineticlink

That graph is near-identical to the graph that was published in David Leadbetter's book on the "Fundamentals of Hogan" (which I posted). One can see that the pelvis rotates faster than the shoulders in the early downswing and that the shoulders eventually rotate about twice as fast as the hips, and the arms eventually rotate twice as fast as the shoulders. This result is very different to the TPI researchers' findings.

Why should there be a doubling of the maximum rotational speed as one proceeds from pelvis => shoulders => arms? I cannot think of a plausible biomechanical reason for this reputed-to-occur phenomenon. Can you?

Note that the text states-: "Once the hips segment reaches maximum speed, deceleration begins to occur. This “braking” action transfers speed to the shoulders segment, which accelerates to a maximum value usually twice that of the hips." The statement implies that the "braking" action of the hips transfers energy and therefore increases the speed of the rotating shoulders. Can anyone provide a rational biomechanical explanation for this amazing assertion that pelvic deceleration in the early-mid downswing will cause the upper torso to rotate faster?

Here is another link to a Zenolink-connected website.

http://www.briankinggolf.com/zenolink.html

Note that it has the following series of statements-: "A normal effective pattern would be one in which the hips segment accelerates first. The hips segment would accelerate to a peak speed at which time it would be rapidly decelerated from within the system. The shoulders segment would accelerate through the point of hips segment peak speed. Through conservation of momentum and the summation of speed the shoulders segment would reach a higher peak speed than that of the hips segment at which time it too would be decelerated."

What do you understand by this claim - "through conservation of momentum and the summation of speed the shoulder segment would reach a higher peak speed"? That statement would seem to imply that COAM is involved in energy transfer between the rotating pelvis and rotating shoulders. However, I cannot understand how COAM can be involved in a system that is actively producing more energy. The concept of COAM only applies to a system where the amount of energy inputted into the system is fixed and the entire system either slows down or speeds up dependent on the distance of the mass of the revolving object from its central axis.

Here is a nice U-tube demonstration of COAM.

Note that the experimenter spins the rotating object until it acquires a certain speed and the system is then left to spin at a certain speed. If the friction at the end points is small, then the rotational speed of the rotating structure will remain constant for a finite period of time. However, during that finite period of time, the rotational speed of the rotating object can be slowed if its shape changes so that it becomes wider (like an Olympic ice skater moving the arms away from her rotating core axis). The key issue is that the system has a "fixed" amount of energy and its rotational speed depends on its physical shape (like an iceskater who is spinning on the ice). COAM has nothing to do with the transfer of energy from one body part to another body part in the early-mid downswing. COAM may affect the speed of movement of the central arm in a double pendulum swing model during the release phase of the peripheral arm, because when the peripheral arm releases the radius of the double pendulum structure (central and peripheral arms) increases, and this must slow the speed of rotation of the central arm - presuming that no more energy is inputted into the double pendulum system after it is torqued by the central torque generator at the start of the pendular swing action. In that sense, one can understand how COAM may cause the arms to slow in the late downswing when the club passively releases (after all the power accumulators have released their energy). COAM cannot be operant in a hitter's action because the hitter is actively driving the clubshaft all the way into impact. The major point that I am making is that the principle of COAM surely cannot be relevant in the early-mid downswing when torso muscles are actively contracting thereby causing active rotation of the pelvis and shoulders, and I have no idea what the author means by the statement "through conservation of momentum and summation of speed".

The second issue relates to the rough accuracy of the TPI researchers' measurement of angular velocity and their general assertion that the shoulders rotate slightly faster than the hips in the early downswing.

I think that there is substantial evidence that this is true. Here are three confirmatory evidentiary sources.

Source 1.

Here is a table from a research study that measured the angular velocity of the pelvis and shoulders at different time points throughout the downswing.

http://perfectgolfswingreview.net/MyersTable.jpg

One can readily see that the shoulders turn faster than the hips at the very start of the downswing and turn much faster than the pelvis at the end of the early downswing (lead arm parallel position) - and these results confirm the findings of the TPI researchers.

Source 2

Here is a series of capture images from a birds-eye view swing video of a very good golfer and I measured his torso-pelvis separation angle throughout the early downswing.



Note that the torso-pelvic separation angle decreases from 48 degrees (at the end-backswing) to 37 degrees (at the end of the early downswing) and that is due to the fact that the shoulders are rotating faster than the pelvis throughout the early downswing - as predicted by the TPI graph and the other research study.

Source 3

Here is another graph from an independent laboratory (Jim McLean' laboratory in Florida run by Rob Neal)



Note that this graph is much more similar to the TPI graph than the kinetic link graph - in the sense that the shoulders start rotating fast from the start of the downswing and travel at roughly the same speed as the pelvis (slightly slower in this measured sequence) while the kinetic link graph predicts that the shoulders don't turn at all in the early downswing.

Jeff.