Bivariate functional principal component analysis of barbell trajectories during the snatch

The purpose of this study was to use bivariate functional principal components analysis (bfPCA) to quantify patterns in barbell trajectories during the snatch and to investigate whether these patterns correlate with weightlifting performance and biomechanical characteristics that characterise weightlifting technique. A motion capture system was used to record three-dimensional barbell trajectories as six weightlifters performed three snatch lifts during a weightlifting competition. Horizontal and vertical barbell positions of all lifts were used as input to a bfPCA. Weightlifting performance was quantified through the ratio of barbell mass/body-mass, whereas biomechanical variables were quantified through peak vertical barbell velocity and acceleration. The bfPCA extracted barbell trajectory patterns related to variations in general forward/backward motion (pattern 1), peak height (pattern 2), and crossing of the vertical reference line during the first pull (pattern 3). Spearman rank correlations showed that pattern 1 correlated positively with weightlifting performance and negatively with peak barbell velocity and acceleration. The opposite results were found for pattern 3. Interpretation of the extracted barbell trajectory patterns and statistical results suggest that better weightlifting performances were characterised by snatch lifts that exhibited general backward shifts and limited forward motions during the first and second pull, regardless of peak heights.