[ThinkingPlus]

2)Jorgensen, "The Physics of Golf", 1994
See Fig 12.1, also last paragraph of Chapter 12 - "...I think the flexing of the shaft forward as the clubhead comes into the ball is a general characteristic of the golf swing. Photographs made with the use of a focal plane shutter must be ignored in this context. There are few photographs in golf literature made with stroboscopic light sources, but of those I've examined, all of them show clubs flexed in this manner."

One thing to keep in mind specifically with Jorgensen and very likely with the others is the model swing on which their analysis is based. Jorgensen found footage of a particular PGA tour professional (unnamed) and used various images to create a mathematical model. He tweaked his model until it matched up well with that single subject. He may also have commented that his model matched reasonably well to other photographs. At this point he played parametric games with his model to see how the various parameters affected swing speed and other swing features.

What is not known with Jorgensen's human test subject, or possibly with the others as well, is whether the golfer was following the impact principles of TGM or not. Just because someone plays professionally or is a top amateur does not mean they swing in the most optimal fashion in the book. Nothing definitive, therefore, can be said about shaft flex before, during, or after impact unless we have a test subject who unquestionably is retaining maximum on plane lag pressure at impact with flat left wrist and bent right wrist.

BTW, I know the above sounds like some mad lady on a soapbox lecturing the crowd. It is not meant to be that way. I tend to get preachy unintentionally. This thread discussion has been very fun and one I have wanted to start for a long time. You just beat me to it! I think the video footage Yoda referred to will be definitive (one way or another). I also agree that whatever the outcome, the FLW & BRW hands leading clubhead at impact with maximum lag pressure golf stroke will always produce the most ball compression and speed. This is too much fun!!!!