KINEMATIC SEQUENCE – CALCULATION METHODS (P3)
Kinematic Sequence Method – TPI 3D
The angular velocities for the kinematic sequence are calculated as follows: Anatomically based local coordinate systems are created in each body segment by digitizing specific bony landmarks; this method is also used for the club. This is a standard biomechanical practice that effectively takes a sensor that is placed anywhere on the segment and “moves” it inside the body to a specific anatomically relevant position and orientation. KINEMATIC SEQUENCE – CALCULATION METHODS (P3)
Example of the Anatomical Digitizing Method S1 is the sensor but T becomes the local coordinate system of the thorax
The angular velocity vector of each segment’s motion is then calculated with respect to the global coordinate system; in the case of an electromagnetic system this is in the middle of the transmitter on the tripod behind the golfer. This vector is then resolved into the local coordinate system of the respective body segment and broken into its coordinates around the three local axes of the segment; the inferior-superior, mediallateral, and anterior-posterior axes. For the pelvis and thorax the angular velocity component around the inferior-superior (up-down) axis is used to represent the rotational velocity of that segment. The lead upper arm was used as the third link in the sequence because of its direct attachment to the thorax and importance in the downswing. The arm and club rotate about an end point in a pendulum motion and not around a center point; hence the angular velocity component around a normal to the instantaneous swing plane was used for these two segments; again derived in the local coordinate system of the specific segment. It is also of interest that no digital filtering was applied during the calculations because the electromagnetic hardware has a high sample rate of 240 Hz (compared to 60 Hz for NTSC video) and produced very clean position and orientation signals. Inappropriate or over smoothing will distort the timing and amplitude of peaks especially near impact.