[Jeff]

Yoda - the yellow lines represent the spinal tilt angle.

The yellow line in photo 2 is only an approximation because I believe that it is impossible to accurately represent the spine position when the golfer is at the end-backswing position - when viewing the golfer from a face-on view. At the end-backswing, the pelvis has rotated about 45 degrees and the shoulders about 90 degrees. That causes the spine to twist in a spiral manner, so it is impossible to draw a single line as being accurately representative of the degree of spinal tilt (of a spiral structure).

I draw my "approximate spine line" as follows. I know that the pelvis rotates 45 degrees in the backswing which shifts the lowest lumbar vertebra to the left. I then start the bottom of my line just left of center (approximately where I think the L5 vertebra is located). I then look for a point at the base of the neck where I imagine the C7 vertebra is located (which is near the blue dot = upper swing center between the shoulder blades), and I draw a straight line between those two points.

Jeff.