[BerntR]

If you reach out a little for the ball the plane of the right forearm (and shaft) at fix will be the turned shoulder plane. So a shoulder turn plane doesn't imply a plane shift.

Elbow plane is defined with the elbow close to the hip.

Those who turn through the ball on the elbow plane usually have a plane shift. Homer says (7-7) that the shoulder planes are the ones concious used while the elbow plane is more - almost totally - subconciously used.

I should probably know why because I think I've had plane shift this year, and a pretty wild one too. But I don't know why. I saw a swing analysis of Sergeo Garcia the other day. He has a very distnict plane shift, and it was basically assessed as a compensation for his having the weight too much towards his heels at address. And also a cause of the rare wild shot that sometimes appeared when Sergeo was under pressure. Of corse all served with a very moderate tone and the deepest respect for Sergio's world class ball striking ability.

The analysis came from the one plane / two plane camp and it seems like some golfers are born one planers while others are natural two planers.