PRACTICAL SIGNIFICANCE
The throwing shoulders of active collegiate baseball pitchers do not exhibit clinically significant acute alterations in glenohumeral joint laxity and stiffness, posterior shoulder tightness, or scapular upward rotation at rest or following a bullpen throwing session.  However, chronic alterations in rotational range of motion (ROM) is present with a near symmetric gain in throwing shoulder external rotation and loss of internal rotation of approximately 10° that does not change significantly following pitching.  Therefore, alterations in these shoulder mobility variables may be early warning signs for the development of shoulder pathology.

STUDY BACKGROUND
Four common factors have been attributed to the pathologic throwing shoulder: 1) increased anterior humeral translation, 2) increased posterior shoulder tightness, 4) internal rotation deficit that exceeds external rotation gain, and 5) loss of scapular upward rotation.  Limited data are available regarding the chronic adaptations in shoulder mobility that occurs as a result of repetitive overhead throwing.  Even fewer data are available that have examined the acute effects of throwing on shoulder mobility.  In the absence of baseline information regarding shoulder mobility adaptations in baseball pitchers, it is difficult to determine their possible contribution towards the development of shoulder pathology.

OBJECTIVE
To evaluate glenohumeral (GH) joint and scapular kinematics in collegiate baseball pitchers at rest and after a pitching sequence to evaluate the acute and chronic effects of throwing on shoulder girdle mobility.

DESIGN AND SETTING
A repeated measures design was used to assess shoulder mobility variables prior to and following a pitching session at collegiate baseball facilities.

SUBJECTS
Forty-four asymptomatic collegiate baseball pitchers (age = 19.2 ± 1.0 years, height = 184.9 ± 5.1 cm, mass = 82.7 ± 8.2 kg, years pitching = 8.5 ± 3.9) from a sample of convenience participated in this study.

MEASUREMENTS
The following dependent variables were measured: 1) GH joint laxity (mm), 2) GH joint stiffness (N/mm), 3) Posterior shoulder tightness {(PST) cm} 4) External rotation (ER), 5) Internal rotation (IR), and 6) Scapular upward rotation (SUR).  Shoulder mobility measures were obtained bilaterally prior to any activity and again after throwing a bullpen session.  GH laxity and stiffness were measured using a LigMaster™ computerized-stress arthrometer (Figure 1), PST was measured using a carpenters square, ER and IR were measured using a goniometer, and SUR was measured using a digital inclinometer (Figure 2).   Separate 2(side) x 3[position (anterior-neutral, anteriorninety, posterior-neutral)] x 2(session) repeated measures ANOVAs were used to assess laxity and stiffness.  Separate 2(side) x 2(session) repeated measures ANOVAs were performed to evaluate PST, ER, and IR. A 2 (side) x 2(session) x 4 (elevation angle) repeated measures ANOVA was utilized to examine SUR.

RESULTS
Pitchers threw an average of 50.2 ±10.8 (range 30-75) pitches.  No significant main effect for laxity was observed for side (P=0.051) or session (P=0.096), but a significant main effect for position was observed (P<.001).  The side x session x position interaction for laxity was nonsignificant (P=0.75).  A significant main effect for stiffness was observed for side (P=0.044), session (P=0.002), and position (P<.001).  The stiffness side x session x position interaction was non-significant (P=0.91).  For PST, the main effect for side (P=0.77) and the side x session interaction (P=0.12) were nonsignificant.  A significant difference between sides was observed for ER (throwing = 105.1 ± 8.7°, non-throwing = 93.8 ± 8.8°; P<.001).  However, the side x session interaction for ER was non-significant (P=0.84).  A main effect for side was observed for IR (throwing =44 ± 8.3°, non-throwing = 54.8 ± 8.6°; P<.001).  The side x session interaction for IR was nonsignificant (P=0.54).  For SUR, the main effect for side (P=0.62) and the side x session x elevation angle interaction (P=0.26) were non-significant.

CONCLUSIONS
Collegiate baseball pitchers demonstrated no significant chronic or acute adaptations in glenohumeral laxity, PST, or SUR.  A statistically significant, but clinically small (<1 N/mm), chronic adaptation in glenohumeral stiffness was observed with no significant acute differences.  Statistically and clinically significant chronic adaptations in ER and IR were present (≥9°), but no acute differences were observed as a result pitching a bullpen session.

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