Three-dimensional kinematic analysis of the golf swing using instantaneous screw axis theory, part 1: methodology and verification

Abstract

A number of recent studies have measured the extent and timing of segment rotation during the golf swing. A promising technique, instantaneous screw axis (ISA) theory, could provide a better expression of segment rotation. In Part 1 of this two-part study, the objectives are to identify the ISA of the pelvis, shoulders and left arm during the downswing, compute segment angular velocity relative to that segment's ISA and verify that ISA theory is a valid tool to analyse segment rotation during the golf swing. Results indicate that for all subjects, at least 71% of marker velocity is a result of rotation about their respective ISA, when averaging results over the duration of the downswing, confirming that motion is primarily rotational. Furthermore, ISA position and orientation of each segment approaches, on average, the expected gross axis of rotation, confirming that motion about the ISA is representative of joint motion.

Three-dimensional kinematic analysis of the golf swing using instantaneous screw axis theory, Part 2: golf swing kinematic sequence

“…This would not only provide the best representation of a segment rotation, but it would also allow for this instantaneous axis to change position and orientation during the motion to reflect changes in the segment's dominant axis of rotation. These finding were confirmed in Part I of this study [10].…”

“…Reflective markers were placed on the subject's body according to the marker placement guide listed in Table 2 and shown in Fig. 2 as described in Part 1 [10]. Briefly, anatomical landmarks were chosen as the most prominent landmarks of each segment, to limit soft tissue artifact [12] and easily identifiable through manual palpations.…”

“…The beginning of the downswing characterized as the transition between the backswing and downswing arcs formed by the club head, and impact were both determined from the displacement of a marker placed on the side of the golf club head midway between the toe and heel. These methodologies were further discussed in Part 1 [10] and were followed in the current study.…”

“…A specific example to golf would be that the rotation of the pelvis should occur about the right leg during the back swing and then about the left leg at impact for a right-handed golfer; use of instantaneous screw axis would show this change in the rotation axis. The methodology of applying ISA theory to the study of the golf swing has been treated in Part 1 [10] of this two-part study.…”

“…Right platform (R) and left platform (L) denote foot placement for the stance of subject, with the line of play in the negative x-axis direction. Figure taken from Part 1[10] …”