Glenohumeral joint and muscles functions during a lifting task

Area of Science:

• Biomechanics
• Human Movement Science
• Orthopedics

Background:

• The shoulder's glenohumeral joint requires intricate muscle coordination for mobility and stability.
• Previous research highlights glenohumeral stability complexity but lacks clarity on muscle-kinematic interactions.
• Understanding these interactions is crucial for diagnosing and treating shoulder dysfunctions.

Purpose of the Study:

• To quantify glenohumeral joint and muscle function during an above-the-shoulder task.
• To investigate how kinematics and muscle activity adapt to ensure joint stability under varying loads.
• To adapt and apply a novel index-based approach for analyzing upper limb joint and muscle behavior.

Main Methods:

• Adapted an index-based approach from lower limb locomotion studies.
• Recruited 40 participants performing a box-lifting task (6 kg vs. 12 kg) from hip to eye level.
• Computed mechanical powers and characterized muscle/degree-of-freedom functions using indices.

Main Results:

• The glenohumeral joint exhibits compliance and a large range of motion.
• Rotator cuff indices confirmed their primary stabilizing role.
• Muscle function adaptations were observed under increased load, favoring joint stability.
• Overall muscle functions demonstrated a complexity in glenohumeral stability beyond the rotator cuff.

Conclusions:

• The glenohumeral joint's function is complex, involving coordinated muscle actions for stability and mobility.
• The adapted index-based approach effectively quantifies joint and muscle behavior in 3D upper limb tasks.
• Findings offer insights into motor control and potential alterations in pathologies or due to external factors like load.