Maximum Shoulder Torque and Muscle Activation During Standing Arm Flexion: Reference Data for Biomechanical and...

Area of Science:

• Biomechanics
• Human Movement Science
• Ergonomics

Background:

• Shoulder joint strength and muscle activation are crucial for understanding overhead reaching.
• Accurate data is needed for ergonomic task design, rehabilitation, and exoskeleton development.

Purpose of the Study:

• To characterize maximum shoulder torque and flexor muscle activation profiles across functional elevation angles in healthy adult males.
• To establish biomechanical reference values for isometric standing conditions.

Main Methods:

• 14 healthy males performed maximum voluntary isometric contractions at 8 arm elevation angles (90-160°).
• Shoulder torque was measured, and electromyography (EMG) was recorded from key shoulder and arm muscles.
• Data was normalized, and statistical analyses (linear regression, mixed-effects models) were applied.

Main Results:

• Maximum shoulder torque significantly declined with increasing elevation angle (R² = 0.99).
• Medial deltoid activation increased, while pectoralis major activation decreased sharply with elevation.
• Anterior deltoid and biceps brachii showed consistent activation across angles.

Conclusions:

• This study provides preliminary biomechanical reference values for shoulder torque and muscle activation in healthy males.
• Findings confirm an inverse torque-angle relationship and distinct muscle activation strategies at higher elevation angles.
• Results can inform ergonomic assessments and exoskeleton design, with caution for generalization to dynamic tasks.