Glenohumeral and Scapulothoracic Rhythms

Central Theme:

The glenohumeral rhythm and scapulothoracic rhythm are coupled actions essential for coordinated shoulder movement. These rhythms involve precise biomechanics in the kinetic and kinematic chains of the upper body and align with respiratory and gait cycles to facilitate efficient motion.

Questions for tonight’s discussion

1. What is the typical movement ratio between the humerus and scapula in the glenohumeral rhythm?
2. Describe the roles of the serratus anterior and trapezius in scapulothoracic rhythm.
3. How does thoracic rotation influence scapular motion during the swing phase of gait?
4. Define planular organization and explain its importance in shoulder mechanics.
5. How do inhalation and exhalation influence scapular position and humeral motion?
6. What is the function of the rotator cuff during arm elevation?
7. Explain the difference in scapular position during the stance and swing phases of gait.
8. How do altered shoulder rhythms affect movement efficiency and injury risk?

1. Thesis Statement

The harmonious relationship between the glenohumeral and scapulothoracic rhythms ensures optimal mobility and stability of the shoulder complex. This coordination integrates with breathing patterns and gait cycles, impacting both stance and swing phases.

 

2. The “Why” Behind the Rhythms

• Efficiency: The coupling of glenohumeral and scapulothoracic rhythms reduces energy expenditure and mechanical stress on the shoulder joint.
• Injury Prevention: Proper alignment and timing minimize impingement and overuse injuries.
• Functional Integration: These rhythms contribute to the seamless transition between upper and lower body movements, particularly in activities like walking, running, or throwing.

 

3. Key Concepts of Glenohumeral and Scapulothoracic Rhythms

A. Glenohumeral Rhythm

1. Definition: The relationship between the humeral head’s movement in the glenoid fossa and the scapula’s position.
2. Ratio of Movement: Typically 2:1 (e.g., for every 2° of humeral elevation, the scapula rotates 1° upward).
3. Biomechanical Actions:
• Flexion/extension.
• Abduction/adduction.
• Internal/external rotation.

B. Scapulothoracic Rhythm

1. Definition: The movement of the scapula over the rib cage during arm motions.
2. Movements Involved:
• Upward/downward rotation.
• Elevation/depression.
• Protraction/retraction.
3. Stabilizing Role: Maintains the glenoid fossa’s alignment with the humeral head.

C. Coupling of the Rhythms

1. The scapulothoracic rhythm supports glenohumeral joint mobility by repositioning the scapula.
2. Both rhythms work together to create a smooth arc of motion during humeral elevation.

4. Biomechanics and Kinetics of the Rhythms

A. Plane of Motion (Planular Organization)

• Sagittal Plane: Flexion and extension.
• Frontal Plane: Abduction and adduction.
• Transverse Plane: Internal and external rotation.
• Scapular Plane (Scaption): A natural oblique plane (30–45° anterior to the frontal plane) that allows for optimal shoulder mechanics.

B. Radiuses of Motion

1. Humeral Radius: The path traced by the distal humerus during arm movements.
2. Scapular Radius: The arc of scapular rotation over the thorax.
3. Trunk Radius: Thoracic extension or rotation complements scapular movements to maintain alignment.

C. Kinematics

• Humeral head moves within the glenoid cavity while scapula adjusts its orientation.
• Example: During shoulder abduction, scapula upwardly rotates, tilts posteriorly, and internally rotates.

D. Kinetics

• Muscles like the serratus anterior, upper trapezius, and rotator cuff stabilize and mobilize the joint.

• Proper force coupling between deltoid and rotator cuff is essential for humeral elevation without impingement.

5. Rhythms in the Gait Cycle

A. Stance Phase

1. Thoracic Position: Stable with mild extension and rotation towards the stance side.
2. Scapular Position: Slight protraction and upward rotation to stabilize the upper limb.
3. Humeral Position: Minimal motion; arm remains close to the body in a flexed, external, and abducted position.
4. Breath Coordination: Abdominals contract (exhalation), creating thoracic stability.

B. Swing Phase

1. Thoracic Position: Rotates opposite to the swing side to counterbalance.
2. Scapular Position: Retraction and downward rotation for arm extension and backward swing.
3. Humeral Position: Backward extension, internal rotation, and abduction.
4. Breath Coordination: Inhalation during backward scap/arm motion aids in thoracic stabilization.

 

6. Integration of Breathing Patterns with Shoulder Rhythms

1. Inhalation:
• Expands the rib cage, allowing scapular depression and downward rotation.
• Enhances thoracic flexion during arm extension. (Intra-thoracic pressure)
2. Exhalation:
• Compresses the rib cage, supporting scapular protraction and upward rotation.
• Facilitates humeral stability during arm acceleration.

7. Practical Applications and Drills

A. Improving Scapulothoracic Rhythm

1. Wall Slides with Serratus Activation: Ensures proper upward rotation.
2. Scapular Clock Exercise: Improves proprioception and movement control.

B. Enhancing Glenohumeral Stability

1. Rotator Cuff Strengthening: External rotation with resistance bands.
2. Overhead Holds: Builds dynamic stability for humeral head control.

C. Gait-Specific Drills

1. Arm Swings with Thoracic Rotation: Coordinates arm motion with trunk movement.
2. Breath-Timed Shoulder Rolls: Synchronizes scapular motion with breathing.

8. Key Terms and Definitions

1. Glenohumeral Rhythm: Coordinated movement of the humerus and scapula during shoulder elevation.
2. Scapulothoracic Rhythm: Movement of the scapula over the thorax in response to humeral motion.
3. Planular Organization: The division of movements into specific planes (sagittal, frontal, transverse, scapular).
4. Kinematics: Study of motion without regard to forces.
5. Kinetics: Study of forces acting on the body.
6. Force Couple: Balanced activation of muscles to produce smooth movement.
7. Swing Phase: The part of the gait cycle when the foot is off the ground.
8. Stance Phase: The part of the gait cycle when the foot is in contact with the ground.

9. References

1. Ludewig, P. M., & Reynolds, J. F. (2009). The association of scapular kinematics and glenohumeral joint pathologies. Journal of Orthopaedic & Sports Physical Therapy, 39(2), 90-104.
2. Kibler, W. B., et al. (2013). Clinical implications of scapular dyskinesis in shoulder injury. British Journal of Sports Medicine, 47(14), 877-885.
3. Neumann, D. A. (2010). Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation. Elsevier.