KINEMATIC SEQUENCE – CALCULATION METHODS (P2)
Kinetic Link Calculation Method cont.
So the kinetic link uses three segmental angular speeds and one joint angular speed. At least the three segmental angular speeds seem intuitively good since the golf swing is usually thought of as rotating around the spine. However on closer look they suffer from out of plane errors since the segment vectors are actually projections on to the PTS plane. If any of these segments (pelvis, upper body or composite arm) tilt out of the PTS plane, that is to say, if they don’t rotate exactly in a plane that is perpendicular to the spine line then angular speed errors will occur. This is especially evident with the composite arm line.
There is another problem with this method and that is the use of the composite arm to represent the third link in the chain. This link is an combination of the motion of the upper arms and forearms of the golfer; it spans the shoulder, elbow and wrist joints; all of which are free to move independently. We at TPI found that this tends to cause this velocity to fluctuate depending on how much the golfer bends the arms and the wrists; quite often it peaks earlier than the upper body even in good golfers. Finally I emphasize that in the kinetic link method, the last link in the chain is the not the club speed but the wrist release speed.