Torque and force production during shoulder external rotation: differences between transverse and sagittal planes

Area of Science:

• Biomechanics
• Human Movement Science
• Orthopedics

Background:

• Joints with multiple degrees of freedom, like the shoulder, exhibit altered muscle moment arm behavior with combined movements.
• Torque production capacity for a given movement varies significantly depending on the plane of motion.

Purpose of the Study:

• To quantify the differences in torque production and resultant force during shoulder external rotation.
• To compare these biomechanical parameters between the transverse and sagittal planes at 90 degrees of shoulder abduction.

Main Methods:

• Eight participants performed shoulder external rotation in the transverse plane using an isokinetic dynamometer and electrogoniometer.
• Six participants performed the same movement in the sagittal plane under identical conditions.
• Torque and resultant force were measured and compared between the two planes.

Main Results:

• External rotation in the sagittal plane yielded significantly greater torque magnitudes compared to the transverse plane.
• Higher resultant forces were also observed during sagittal plane external rotation.
• The enhanced performance in the sagittal plane is hypothesized to be due to prestretching of the infraspinatus and teres minor muscles.

Conclusions:

• The plane of movement critically influences shoulder external rotation torque and force production.
• Sagittal plane execution, potentially due to muscle pre-stretch, offers a biomechanical advantage for external rotation.
• These findings have implications for understanding shoulder function and designing rehabilitation or training programs.