Shoulder Strength and Total Arc Range of Motion: Associations With Upper-Extremity Joint Kinetics and Ball Velocity...

Adolescent baseball pitchers are vulnerable to upper-extremity injuries because of the repetitive, high-stress nature of throwing movements. While shoulder strength and range of motion (ROM) are commonly measured, they are often interpreted in isolation during injury prevention assessments.

To determine the relationship between clinical measures (shoulder ROM and strength) and throwing arm joint kinetics in adolescent baseball pitchers.

Descriptive laboratory study.

This study was conducted in a laboratory setting. A total of 43 adolescent baseball pitchers (age, 15-18 years) were recruited through convenience sampling. Participants underwent clinical assessments of shoulder ROM and isokinetic concentric strength testing. Pitching biomechanics were analyzed to obtain elbow valgus torque, shoulder distraction force, shoulder internal rotational (IR) torque, and ball velocity. A stepwise linear regression analysis was performed to assess shoulder strength and ROM as predictors of pitching kinetics and ball velocity.

A stepwise regression analysis showed that elbow valgus torque (92.1 ± 24.9 N·m) was positively associated with increased shoulder IR strength at 60 deg/sec and negatively associated with total arc ROM (IR strength, 68.3 ± 17.3 N·m; total arc, 172.8°± 19.2°; adjusted R ² = .258; P < .001). Peak shoulder distraction force (1238.9 ± 361.2 N) was positively associated with shoulder external rotation (ER) strength at 60 deg/sec (41.3 ± 10.8 N·m; β = .465; adjusted R ² = .197; P = .002). Peak shoulder IR torque (113.7 ± 37.4 N·m) was positively associated with shoulder IR strength (β = .421; adjusted R ² =.157; P = .005). Higher ball velocity (125.9 ± 8.7 km/h) was linked with higher shoulder IR strength (β = .390; adjusted R ² =.131; P = .010). There were moderate to strong positive relationships between ball velocity and pitching kinetics (Pearson's r value: valgus torque, 0.603; distraction force, 0.594; shoulder IR torque, 0.865; P < .001).

Pitchers with greater shoulder IR strength and reduced total arc ROM demonstrated increased elbow valgus torque at maximal shoulder ER during pitching. Although IR strength is crucial for generating ball velocity, maintaining total arc ROM within an optimal range will help reduce elbow joint stress. In addition, shoulder ER was positively associated with peak shoulder distraction force. Monitoring ER strength may help identify potential fatigue or imbalance, allowing for timely clinical attention.