Repetitive throwing at high velocities leads to altered range of motion (ROM) in the dominant shoulder compared with the nondominant shoulder in overhead-throwing athletes. Loss of glenohumeral internal rotation (IR), or glenohumeral internal-rotation deficit (GIRD), is associated with shoulder injuries. Therefore, GIRD should be evaluated during the clinical examination of the thrower's shoulder.
To assess glenohumeral ROM in competitive baseball and softball athletes at 3 intervals over the course of an athletic season in order to (1) examine changes in ROM over time and (2) monitor the prevalence of GIRD.
Observational, repeated-measures study.
Collegiate athletic training room.
Patients or Other Participants:
Forty-eight healthy National Collegiate Athletic Association (NCAA) Division I or Division II athletes (age = 19 ± 1 years, height = 174 ± 14 cm, mass = 77.8 ± 18.1 kg; 19 softball, 29 baseball players).
Main Outcome Measure(s):
We measured glenohumeral IR, external rotation (ER), total arc (ER + IR), and GIRD at 3 times: prefall, prespring, and postspring. We calculated GIRD in 2 ways: as the difference in IR between dominant and nondominant shoulders and as the percentage of the total arc.
In the dominant shoulder, ER increased during the season (F2,96 = 17.433, P < .001), but IR remained the same (F2,96 = 1.839, P = .17). The total arc in the dominant shoulder increased between time intervals (F2,96 = 14.030, P < .001); the mean difference between prefall and postspring measurements was 9.694° (P < .001), and the mean difference between prefall and postspring measurements was 10.990° (P < .001). In the nondominant shoulder, ER increased over the season (F2,96 = 23.395, P < .001), but IR did not change over the season (F2,96 = 0.087, P = .90). The total arc in the nondominant shoulder increased between prefall and prespring measurements and between prefall and postspring measurements (F2,96 = 18.552, P < .001). No changes were noted in GIRD over time. However, more athletes with GIRD were identified with the GIRD (IR difference) calculation in prefall (n = 6) than in prespring (n = 1) and postspring (n = 4) (Cochran Q = 5.2, P = .07). In addition, more athletes with GIRD were identified with the GIRD (% total arc) calculation in postspring (n = 6) than in prefall (n = 5) or prespring (n = 4) (Cochran Q = 2.6, P = .27).
Healthy NCAA Division I and Division II athletes did not display changes in glenohumeral IR over an athletic season. However, they gained in ER and total arc during the season in both shoulders. Future researchers should investigate changes over multiple seasons. The 2 methods of calculating GIRD identified different athletes as having GIRD, indicating that additional investigation is warranted to determine the clinical benefits of each method.