Shoulder-elbow coordination in the transverse plane during badminton forehand drive depending on training status using vector coding analysis.

To determine how training status influences shoulder and elbow coordination in the transverse plane during the badminton forehand drive, using vector coding and coupling angle mapping. Fifteen trained and fifteen untrained people participated. Motion capture recorded upper limb kinematics during forehand drives. Shoulder internal/external rotation and elbow pronation/supination angles were obtained via inverse kinematics. Data were trimmed from maximal shoulder external rotation to shuttlecock impact and analyzed with vector coding to compute coupling angles and classify eight coordination categories, followed by coupling angle mapping. Range of motion was computed for shoulder, elbow, and wrist. Group differences were tested using multivariate and univariate analyses, and principal component analysis summarized phase counts. Trained participants showed larger upper limb range of motion across several planes and distinct coordination sequences that began predominantly in Anti-Phase and transitioned to In-Phase near impact, with shoulder internal rotation frequently dominant. Untrained participants more often began In-Phase and ended Anti-Phase, indicating a different inter joint sequencing pattern. Phase count analysis and the first principal component differentiated groups, with trained participants showing more In-Phase Shoulder Internal Rotation Dominancy and fewer distal dominant phases. Patterns were visualized with coupling angle mapping. Coordination of the shoulder and elbow in the transverse plane differs by training status during the forehand drive. Trained participants use a strategy that separates and then synchronizes joint motions, favoring proximal dominance to support efficient kinetic transfer and racket acceleration. These findings provide a biomechanical basis for coaching that develops In-Phase shoulder-led coordination while acknowledging variability.