Relationship between trunk and pelvic rotation angles during throwing and the Kerlan–Jobe Orthopedic Clinic score in quarterbacks in American football

abstract: Background: Quarterbacks (QBs) in American football frequently perform repetitive overhead throwing, which can lead to shoulder and elbow injuries. Effective control of trunk and pelvic movements is considered crucial for minimizing shoulder and elbow joint stress during throwing. The Kerlan–Jobe Orthopedic Clinic (KJOC) score is a self-perceived index of shoulder and elbow function and level of competition in overhead athletes. However, the relationship between trunk and pelvic movements during throwing and the KJOC score among QBs remains unclear. This study aimed to examine the association between trunk and pelvic motion during the QB throwing sequence and the KJOC score. Methods: A total of 11 healthy QBs were enrolled in this study. Each participant completed 5 throws at distances of 18.2 m (20 yards) and 27.4 m (30 yards). Throwing mechanics were analyzed using the PitchAI application, focusing on trunk and pelvis rotation (toward the nonthrowing and throwing sides) and hip–shoulder separation angles. These angles were measured at 3 key phases: stride foot contact during the early cocking phase, maximum shoulder external rotation during the late cocking phase, and ball release. Participants also completed the KJOC questionnaire, with higher scores indicating better self-perceived index of shoulder and elbow function or level of competition. Correlations between throwing mechanics and KJOC each item and total scores were assessed using Spearman's rank correlation coefficient. Results: Trunk rotation at maximum shoulder external rotation during 20-yard throws and hip–shoulder separation at stride foot contact during 30-yard throws were positively correlated with KJOC Item 3 (rs = 0.709; P = .015 and rs = 0.662; P = .026, respectively). Pelvic rotation at ball release during 30-yard throws showed a positive correlation with KJOC Item 4 (rs = 0.760; P = .007). Conclusion: This study suggests a relationship between trunk and pelvic rotational movements during a quarterback's throw and certain aspects of subjective shoulder and elbow function.