AbstractsBiology & Animal Science

Decreases in glenohumeral (GH) rotation motion and rotator cuff strength have been linked to multiple pathologies in the throwing arms of baseball pitchers, but a full understanding of the shoulder mechanisms affected by a total arc of motion deficit (TAMD) has not yet been achieved. This study was designed to quantify the effects that this loss in range of motion has on GH joint laxity and eccentric external and internal rotation strength measures. We recruited 47 intercollegiate baseball pitchers with no history of shoulder or elbow surgery, and assigned them to either a TAMD group or a Non-TAMD group based on the extent of their loss of rotational motion at the shoulder. Eccentric internal and external rotation peak force values were evaluated in the middle 70% of the pitchers' available rotational range of motion with an isokinetic dynamometer, while anterior and posterior GH joint laxity and stiffness were assessed with a multijoint arthrometer under a 150N load applied at a rate of 15-19 N/s, with stiffness calculated as the slope of the force displacement curve following the inflection point representing the point of soft tissue compression. We found significant differences in the stiffness measures when comparing the anterior to the posterior directions in both the dominant (22.64 ± 5.02 N/mm and 28.72 ± 7.18 N/mm, p < 0.001) and non-dominant arms (23.01 ± 5.66 N/mm and 29.31 ± 8.07 N/mm, p < 0.001). There was also a significant Group x Direction interaction for GH laxity and this finding was attributed to the fact that that TAMD group had significantly less posterior translation than did the Non-TAMD group (p <0.05). Significant differences were also found for IR, ER and strength ratio measures (p < 0.001). The ER/IR strength ratio (86.2 ± 23.3% vs. 47.0 ± 7.8%) and ER eccentric peak torque (0.410 ± 0.088 Nm/kg BW vs. 0.295 ± 0.049 Nm/kg BW) were significantly greater in the dominant arm, while IR eccentric peak torque (0.488 ± 0.088 Nm/kg BW vs 0.636 ± 0.101 Nm/kg BW) was significantly higher in the non-dominant arm. Internal rotation eccentric peak torque measures (0.488 ± 0.088 Nm/kg BW) were significantly higher than any of the isometric measures (p < 0.001). Testing of the ER torques showed that eccentric measures (0.410 ± 0.088 Nm/kg BW), and isometric measures at 0°(0.386 ± 0.132 Nm/kg BW) and 30° (0.366 ± 0.122 Nm/kg BW) were significantly higher than the 60°(0.247 ± 0.087 Nm/kg BW) and 90° (0.188 ± 0.073 Nm/kg BW) measures (p < 0.001). Isometric ER/IR strength ratios at 0° and 30° were significantly lower than at the 0° and 30° testing positions (p < 0.01). These findings suggest that the type of muscle action and GH joint angle were responsible for differences observed in internal and external rotation peak torques. The loss of shoulder rotational range of motion in collegiate pitchers did not affect their eccentric peak torque production, but was related to increased posterior GH capsuloligamentous laxity, although the clinical significance of this difference is presently unknown.