What is shoulder flexion?

Shoulder Flexion: Definition and Biomechanics

Shoulder flexion is the forward movement of the arm in the sagittal plane, raising the arm anteriorly from the anatomical position, involving complex coordination between the glenohumeral joint, scapula, and clavicle. 1

Anatomical Basis

The shoulder is a ball and socket joint that allows for exceptional mobility at the expense of stability. Key components involved in shoulder flexion include:

• Glenohumeral joint: The primary shoulder joint where the humeral head articulates with the glenoid fossa
• Scapulothoracic articulation: Movement of the scapula on the thoracic wall
• Sternoclavicular and acromioclavicular joints: Allow for clavicular movement during arm elevation

Biomechanics of Shoulder Flexion

During shoulder flexion, several coordinated movements occur:

• Glenohumeral motion: The humerus moves anteriorly in the sagittal plane
• Scapular motion: The scapula undergoes upward rotation, posterior tilting, and internal rotation relative to the clavicle 2
• Clavicular motion: Includes elevation, retraction, and posterior axial rotation 2

Range of Motion

Normal shoulder flexion allows the arm to be raised forward and upward approximately 180 degrees from the anatomical position. This motion occurs in the sagittal plane, perpendicular to the coronal plane of abduction.

Muscle Activation Patterns

Multiple muscles contribute to shoulder flexion:

• Primary flexors: Anterior deltoid, pectoralis major (clavicular head), and coracobrachialis
• Scapular stabilizers: Serratus anterior, upper and lower trapezius provide scapular lateral rotation 3
• Rotator cuff involvement: Supraspinatus, infraspinatus, and to a lesser extent, subscapularis 3

Research shows that supraspinatus and anterior deltoid activate simultaneously before movement begins, suggesting they both initiate the flexion motion 3.

Clinical Significance

Understanding proper shoulder flexion mechanics is crucial for:

1. Injury prevention: Proper technique reduces strain on the shoulder complex
2. Rehabilitation: After shoulder injuries or surgeries, restoring normal flexion patterns is essential
3. Ergonomic positioning: For occupational tasks requiring overhead work

Potential Complications

Improper shoulder flexion mechanics can lead to:

• Impingement syndromes: When the rotator cuff tendons are compressed
• Rotator cuff injuries: Particularly when flexion is performed with excessive load
• Scapular dyskinesis: Abnormal scapular movement patterns during arm elevation

Proper Technique for Assessment

When assessing shoulder flexion:

• Patient should be in sitting position with 90° elbow flexion 1
• The arm should start in neutral position alongside the body
• Movement occurs in the sagittal plane, raising the arm forward and upward
• For dynamic examination, both active and passive movement should be assessed 1

Important Considerations

• Shoulder flexion involves medial rotation of the humerus in most individuals 4
• Women and men may demonstrate different rotation patterns during active shoulder flexion 4
• Thoracic spine position significantly affects scapular movement during shoulder flexion 5
• When performing shoulder flexion exercises, the arm should ideally move within a 45° arc from the midline to minimize strain on the shoulder 1

Understanding these biomechanical principles is essential for proper assessment, treatment, and rehabilitation of shoulder conditions.