Pitching shoulder passive flexibility: torque-angle analysis for external rotation and internal rotation

Area of Science:

• Sports Medicine
• Biomechanics
• Orthopedics

Background:

• Pitching involves repetitive, high-velocity arm movements, leading to adaptations in shoulder biomechanics.
• Understanding bilateral shoulder differences is crucial for injury prevention and performance optimization in baseball pitchers.

Purpose of the Study:

• To investigate significant bilateral differences in passive shoulder flexibility between throwing and non-throwing shoulders in pitchers.
• To analyze novel measures of shoulder flexibility: resistance onset angle (ROA), rotational stiffness, and torque at end range of motion (ROM).

Main Methods:

• A custom device was utilized to measure passive external rotation (ER) and internal rotation (IR) flexibility.
• Thirty upper-level pitchers (Division I and minor league) participated in the bilateral analysis.
• Shoulder ROM, stiffness, and torque were recorded with the arm abducted 90° and elbow flexed 90°.

Main Results:

• Significant bilateral differences were found for all measured variables (p < 0.01).
• The throwing shoulder demonstrated increased ER ROA, ER stiffness, ER torque, and IR stiffness, alongside decreased IR ROA and increased IR torque.
• Resistance onset angle (ROA) showed strong correlations with end ROM (ER: r=0.85, IR: r=0.86), while stiffness correlations were weaker.

Conclusions:

• Pitching leads to substantial bilateral asymmetries in shoulder passive flexibility, stiffness, and torque.
• These findings highlight the unique demands placed on the throwing shoulder and may inform injury risk assessment and rehabilitation strategies.
• ROA appears to be a strong predictor of end range of motion in the pitching shoulder.