[Jeff]

dkerby

You seem to define the center of mass as the area around the navel. In that sense, Hogan did move his center of mass slightly leftwards in the final stage of the backswing (as seen in image 3 on page 41). However, that doesn't mean that 70% of Hogan's total body mass was on the left foot at the end-backswing position. The center of mass can be slightly leftwards of the stance center, but the proportion of total body mass favoring the right side versus left side has to also factor in the weight of the upper torso, two arms and head.

You also wrote-: "When the hips are turned back to the left, this tightens the muscles between the hips and the shoulders just a notch more-something like the way a fellow gives each lug that little extra tightening twist when he's changing a tire. Maximum tension in the muscles betwee the hips and the shoulders produces maximum speed."

I personally believe that your theory that increasing the stretch of the torso muscles - by moving the pelvis before the upper body (what Jim McLean calls the dynamic X-factor) - produces maximimum swing power is a theory without adequate scientific evidentiary support.

I wrote a review paper on Jim McLean's X-factor, and I used this photo to make a point.




The torso muscles stretched when the pelvis moves before the upper torso is shown in green. Those muscles are essentially the abdominal oblique muscles on the right-lateral side of the mid-torso. I personally don't believe that stretching those few (limited) muscles plays a large role in generating pivot power in the downswing. However, I do think that kinetic sequencing is important and I do that think that one should start the downswing with a hip shift-rotation movement before rotating the shoulders - but I think that the primary reason relates to the concept of i) taking up spinal slack, and ii) getting a balanced sequential torso rotation (like a figure skater spinning on the ice - the spin has to start from the bottom-up). I personally think that the stretch factor concept (stretching eccentrically loaded torso muscles muscles by a small amount) plays a minor role in maximising swing power.

Jeff.