Loss Of Glenohumeral Range Of Motion And Its Effects On Eccentric Strength In Intercollegiate Pitchers

Abstract

Deficits in glenohumeral joint rotational range of motion (ROM) and strength in baseball pitchers’ shoulders have been linked to increased risk of musculoskeletal injury. Total arc of motion deficit (TAMD) is an objective parameter that involves the comparison of bilateral shoulder internal rotation (IR) and external rotation (ER) ROM values as a measure of soft tissue changes at that joint. PURPOSE: To determine whether TAMD in the throwing shoulder, when compared to the non-throwing shoulder, affected the eccentric strength of IR and ER muscles of the glenohumeral (GH) joints of intercollegiate baseball pitchers. METHODS: 47 male pitchers (age, 19.8+1.2 yrs; hgt, 183.9+5.5 cm; mass, 85.7+10.2 kg; pitching experience, 9.9+2.8 yrs) were recruited to this study and assigned to 1 of 2 groups: 24 pitchers with >10° side-to-side differences in total rotational motion were assigned to the TAMD group, while 23 pitchers with less than 10° side-to-side ROM differences qualified for a non-deficit group (Non-TAMD). We measured eccentric IR and ER peak torques at 300o/sec bilaterally with an isokinetic dynamometer. RESULTS: We observed higher ER/IR strength ratios of the dominant arms when compared to the non-dominant arms of pitchers in both the TAMD (85.2%+24.3% and 45.4%+7.3%) and non-TAMD groups (87.3%+22.8% and 48.5%+8.1%) (p<0.001). There were no significant differences between the normalized TAMD and non-TAMD dominant arm eccentric IR torques (0.497+0.073 Nm/kg BW vs. 0.478+0.062 Nm/kg BW) or eccentric ER torques (0.407+0.082 Nm/kg BW vs. 0.411+0.077 Nm/kg BW) (p>0.05). Dominant arm eccentric 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 both significantly greater than in the non-dominant arm (p<0.05). Internal rotation 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 (p<0.05). CONCLUSIONS: We found ER/IR ratios that were significantly higher in the dominant arms, but no significant differences in ER or IR eccentric strength between the TAMD and Non-TAMD groups. Loss of shoulder rotation ROM did not have a significant effect on the production of IR and ER eccentric torques at the GH joint in this sample of intercollegiate pitchers.