Validation of Markerless Motion Capture Against a Marker-based Reference for Pelvis and Upper Torso Kinematics During a Golf Swing

Sammanfattning

Markerless motion capture has the potential to make sports movement analysis more practical by estimating body motion from video instead of using reflective markers. However, before markerless systems can be used confidently for demanding sports movements, they need to be validated against established marker-based methods. This thesis focuses on the golf swing, which is a fast and rotational movement where pelvis and upper torso kinematics are important for describing trunk rotation and body coordination. The thesis consists of one article that evaluates the ELVA markerless motion capture system against a Vicon Nexus marker-based reference system during full golf swings. Seven golfers performed repeated swings with a 6 iron and a driver while both systems recorded simultaneously at 250 Hz. The analysis focused on pelvis and upper torso kinematics. Since no single golf-specific acceptable-error threshold was identified, the markerless system was evaluated using several criteria, including disagreement magnitude, systematic bias, phase-specific differences, and within-subject trial-to-trial variability. The results showed that the markerless system captured the general pelvis and upper torso movement patterns, but agreement with the marker-based system depended on segment, movement plane, and swing phase. Waveform RMSE ranged from 3.9° to 6.8° for the upper torso and from 4.4° to 7.8° for the pelvis. The largest disagreements occurred during the late downswing and around impact, especially for transverse-plane rotation. Within-subject trial-to-trial variability was generally similar between systems. Overall, the markerless system appears useful for describing general golf-swing movement patterns and for repeated within-system assessment in applied settings. However, it should not be treated as directly interchangeable with the marker-based system when exact pelvis and upper torso angle values are required.