Background and objectives: Glenohumeral joint internal rotation deficit (GIRD) is commonly observed in the dominant arm of baseball pitchers and is limited by horizontal adduction motions. We inferred that when pitchers' generation of internal shoulder rotation and horizontal adduction activity is limited, they may generate compensation movements in other body parts. This study aims to investigate whether pitchers with GIRD generates trunk compensation during pitching where pitching targets were on the lower corner of their non-dominant side.
Design: Case-control study.
Setting: Elite senior high school baseball.
Participants: Twenty-five senior high school baseball pitchers participated in this study. Twelve pitchers with GIRD were assigned to the experiment group, and the remaining 13 participants to the control group.
Main outcome measures: Glenohumeral internal/external rotation of both arms and internal/external rotation of the bilateral hip joints were measured. The kinematic values of the trunk when pitching to a target were measured using high-speed infrared cameras.
Results: Pitchers with GIRD exhibited significantly greater upper trunk rotation toward the non-dominant side when a baseball was released from their hand (27.39 ± 6.62 degrees), compared with non-GIRD pitchers (20.42 ± 5.97 degrees) (p < 0.05). The total rotation of the pivot leg of pitchers with GIRD (67.54 ± 7.84 degrees) was significantly smaller than that of pitchers without GIRD (74.00 ± 7.07 degrees) (p < 0.05).
Conclusions: GIRD in the dominant arm affected upper trunk rotation during pitching and was associated with the hip range of motion. Future studies could conduct a longitudinal study regarding the relationship between GIRD and other joint injuries of the lower limbs.
Keywords: baseball; biomechanics; glenohumeral joint internal rotation deficit; kinematics; pitching.