[HungryBear]

A big hello to everyone @ LBG (first post from a long-time though infrequent visitor).

The other day I got into a (non-TGM) discussion on the biomechanics of the golf swing. Part of that discussion was the 'plane' of the swing and subsequently the TGM principle) that the clubshaft is on-plane if either:
1. The butt end of the Clubshaft is pointing at the Line;
2. The length of the Clubshaft is parallel to the Line; or
3. The head end of the Clubshaft is pointing at the line.

From a biomechanics point of view we could not 'prove' (or disprove) why this is the case (as opposed to for example the opinion that the shaft is on plane when parallel to the inclined (address) plane throughout the swing). Reading through the relevant sections of TGM just now, I still can't substantiate as to WHY mr. Kelley defined being on-plane as he did.

Can anyone shed light on this? I'd very much like to know the foundation on which the TGM on-plane principle is based (preferably from either a mechanical physics or biomechanical pov).

This gets me wondering?
The requirement is that there be a valid plane but I do not see a "the" plane. so the requirement can be met even with a plane shift if the shift maintains a valid plane ie. the same line. Just thought, I may still be all messed-up