Two-dimensional methods have been used to compute trunk kinematic variables (flexion/extension, lateral bend, axial rotation) and X-factor (difference in axial rotation between trunk and pelvis) during the golf swing. Recent X-factor studies advocated three-dimensional (3D) analysis due to the errors associated with two-dimensional (2D) methods, but this has not been investigated for all trunk kinematic variables. The purpose of this study was to compare trunk kinematic variables and X-factor calculated by 2D and 3D methods to examine how different approaches influenced their profiles during the swing. Trunk kinematic variables and X-factor were calculated for golfers from vectors projected onto the global laboratory planes and from 3D segment angles. Trunk kinematic variable profiles were similar in shape; however, there were statistically significant differences in trunk flexion (–6.5 ± 3.6°) at top of backswing and trunk right-side lateral bend (8.7 ± 2.9°) at impact. Differences between 2D and 3D X-factor (approximately 16°) could largely be explained by projection errors introduced to the 2D analysis through flexion and lateral bend of the trunk and pelvis segments. The results support the need to use a 3D method for kinematic data calculation to accurately analyze the golf swing.
Aimée C. Smith, Jonathan R. Roberts, and Stephanie E. Forrester are with the Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, United Kingdom. Aimée C. Smith is also with the Institute for Sports Research, Nanyang Technological University, Singapore. Eric S. Wallace is with the Sport and Exercise Sciences Research Institute, University of Ulster, Newtonabbey, Northern Ireland. Pui Kong is with the Physical Education and Sports Science Academic Group, National Institute of Education, Nanyang Technological University, Singapore.