Variability of in-game markerless and laboratory marker-based baseball pitching biomechanics

Traditionally, baseball pitching biomechanics have been analyzed in controlled laboratory settings. However, with recent technological advancements, markerless motion capture has made capturing and analyzing in-game pitching biomechanics possible. Pitchers typically throw slower in a laboratory setting than they do in an in-game setting, and it is unknown if pitching biomechanics, including the variability of pitching biomechanics, change between environments. Thus, the purpose of this study was to compare pitching variability between marker-based data captured in a typical laboratory setting and markerless data captured in a typical in-game setting. It was hypothesized that pitching kinematics measured with in-game markerless technology would produce greater variability. Data from 30 collegiate baseball pitchers captured in a biomechanics laboratory were compared to data for 30 NCAA Division I pitchers captured using markerless motion capture during competitive games. Within-subject pitching variability was defined as the standard deviation of the pitcher's kinematics over 10 fastballs. Of the 10 kinematic parameters analyzed, variability was significantly greater for in-game markerless data for two parameters (maximum shoulder external rotation and elbow flexion at that instant). Mean values showed large differences between the markerless and marker-based data, consistent with previously published research. This study provides initial evidence that baseball pitching variability is relatively similar between in-game markerless and in-laboratory marker-based settings.