What is horizontal flexion?

Horizontal Flexion

Horizontal flexion is a movement of the shoulder joint where the arm moves in a horizontal plane from an abducted position toward the midline of the body, with the elbow bent at 90 degrees. 1

Definition and Mechanics

Horizontal flexion (also called horizontal adduction) occurs when:

• The arm is positioned at approximately 90 degrees of shoulder abduction
• The movement happens in the transverse/horizontal plane
• The arm moves forward across the body from a position of lateral extension

This motion is distinct from standard shoulder flexion, which occurs in the sagittal plane when raising the arm forward.

Anatomical Considerations

Muscles Involved in Horizontal Flexion

The primary muscles responsible for horizontal flexion include:

• Anterior deltoid (primary horizontal flexor) 2
• Pectoralis major (largest horizontal flexion moment arm when the humerus is elevated 90 degrees) 2
• Subscapularis (may contribute to horizontal flexion) 1

Opposing Muscles (Horizontal Extension)

Muscles that perform the opposite movement (horizontal extension) include:

• Posterior deltoid
• Infraspinatus
• Teres minor 2

Clinical Assessment

When assessing horizontal flexion in clinical settings:

• Patient positioning: The patient is typically seated or standing with the arm abducted to 90 degrees and the elbow flexed to 90 degrees 1
• Movement pattern: The patient moves the arm horizontally across the body toward the midline
• Range of motion: Normal range is approximately 135 degrees from the starting position

Clinical Significance

Understanding horizontal flexion is important for:

1. Shoulder pathology assessment: Limitations in horizontal flexion may indicate:

   • Posterior capsule tightness
   • Rotator cuff pathology
   • Acromioclavicular joint disorders

2. Rehabilitation protocols: After shoulder injuries or surgeries, horizontal flexion exercises are often included in rehabilitation programs to restore normal shoulder function 1

3. Muscle recruitment patterns: During horizontal flexion, there is coordinated activation of multiple shoulder muscles, with the anterior deltoid and pectoralis major showing the highest activity levels 3

Practical Applications

• Ultrasound assessment: When performing shoulder ultrasound, the anterior transverse scan in maximal internal rotation allows visualization of the supraspinatus tendon 1

• Exercise prescription: Horizontal flexion exercises are commonly used in rehabilitation to strengthen anterior shoulder muscles and improve functional movement patterns

• Occupational considerations: Activities requiring repetitive horizontal flexion may contribute to shoulder overuse injuries, particularly when combined with internal rotation 1

Potential Dysfunctions

• Limited horizontal flexion: May indicate posterior capsule tightness or posterior rotator cuff pathology
• Painful horizontal flexion: Often associated with subacromial impingement, acromioclavicular joint pathology, or anterior shoulder instability
• Excessive horizontal flexion: May indicate anterior capsular laxity or instability

Understanding the biomechanics of horizontal flexion is essential for proper assessment and treatment of shoulder disorders, as well as for designing effective rehabilitation programs for patients with shoulder dysfunction.