Shoulder and Scapular Kinematics during the Windmill Softball Pitch: The Effect of Fatigue

OBJECTIVES: Pitch count has been studied extensively in the overhand throwing athlete. However, pitch count and fatigue have not been systematically evaluated in the female windmill (underhand) throwing athlete. Direct kinematic measurements of the glenohumeral and scapulo-thoracic joint have not to be correlated and determined. The purpose is to measure scapular kinematics for the high school female windmill softball pitcher and identify kinematic adaptions and changes in pitching performance due to fatigue. METHODS: Eight female high school softball pitchers without previous shoulder injury were enrolled. Three-dimensional (3D) motion of the humerus, scapula and trunk were recorded with surface markers at 250 Hz. Marker placement and the anatomical calibration of bony landmarks followed recommendations by the ISB (Wu et al. 2005) and Kontaxis et al (2009). A custom marker cluster was used to dynamically track the scapula (Karduna et al. 2001). The pitching mound was at regulation distance (43’) from the strike zone target. All athletes completed 105 pitches in sets of 15 with a rest of 5 minutes between sets. Ball speed recorded with a radar gun, 3D angular rotations of the glenohumeral joint, scapulo-thoracic joint and thorax with respect to the room were calculated for all throws. The last five pitches of every set were averaged for analysis. RESULTS: Ball speed (Figure 1, n=8 subjects) and peak glenohumeral, scapulo-thoracic and thoracic angular rotations (n=4 subjects) were consistent across all sets. Examples of kinematics at two of these joints are presented across all sets (Figure 2, n=4). Data across all planes demonstrated similar consistency. CONCLUSION: This study presents a systematic protocol for the study of fatigue during windmill softball pitching. To our knowledge, this is one of the first studies to analyze glenohumeral as well as scapulo-thoracic kinematics during this task. The consistency in the glenohumeral, scapulo-thoracic and torso kinematics during the throwing protocol demonstrates that despite completing 105 pitches, these athletes are able to maintain shoulder kinematics and ball speed during the underhand pitch. This contrasts to the common observation that male overhand pitchers fatigue around 90 pitches.