How Do the Shoulder Blade, Spine and Rib Cage Influence Throwing

How Do the Shoulder Blade, Spine and Rib Cage Influence Throwing
Photo by Nino Liverani / Unsplash

The shoulder blade (scapula), spine, and rib cage all play important roles in the arthrokinematics and kinematics of shoulder motion. Understanding how they work together is crucial for proper shoulder function, especially in activities that require high-level throwing, such as playing quarterback. The shoulder experiences tremendous load when throwing and serves as the first area where there is a kinetic transmission of force from the chain into the arm.

Important Anatomy

Scapula: The scapula serves as the attachment point for many muscles involved in shoulder movement. It provides a stable base for the shoulder joint and acts as a platform for muscle force transmission. During shoulder motion, the scapula needs to move in coordination with the arm to maintain optimal alignment and stability.

Thoracic Spine: The thoracic spine, which is the middle and upper back region, plays a significant role in shoulder function. It provides a base of support for the shoulder girdle and facilitates coordinated movement between the scapula, rib cage, and arm. Proper mobility of the thoracic spine allows for optimal positioning and movement of the scapula, which in turn affects shoulder mechanics.

Rib Cage: The rib cage is attached to the thoracic spine and acts as a foundation for the scapula and therefore the positioning of the shoulder joint. It provides stability and contributes to overall posture, while allowing a base for the scapula to sit upon and tilt. The position of the ribs and the ability to expand the chest play a role in optimizing shoulder mechanics.

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Important Mechanics

Scapular Coupling: Scapular force coupling refers to the coordinated movement of the scapula and the humerus (upper arm bone) during shoulder motion. Proper scapular coupling is crucial for maintaining the optimal alignment of the shoulder joint, preventing shoulder impingement and maximizing shoulder stability. In throwing, the scapula needs to rotate and upwardly/posteriorly tilt in sync with the arm movement to provide a stable base for powerful and accurate throws. This rotation works as a glide along the rib cage, and speaks to the importance of proper thoracic mobility. Dysfunctions in scapular coupling can lead to inefficient shoulder mechanics, reduced power production/performance and an increased risk of injury.

The force couple of the scapula for elevation and external rotation of the humerus (upper arm bone) during throwing involves the coordinated action of several muscles. A force couple refers to a group of muscles that work together to create a balanced force around a joint. In the context of upward rotation of the humerus during throwing, the force couple primarily includes the following muscles:

Serratus Anterior: The serratus anterior muscle is located on the side of the rib cage and plays a significant role in upward rotation of the scapula. It attaches to the inner border of the scapula and acts as a primary protractor and upward rotator of the scapula. During the throwing motion, the serratus anterior contracts to initiate and maintain the upward rotation of the scapula, allowing for proper positioning and stability of the shoulder joint. It is often under trained and under developed.

Upper Trapezius: The upper fibers of the trapezius muscle, which are located in the upper back and neck region, contribute to scapular upward rotation. When activated, the upper trapezius assists in elevating the scapula and works in conjunction with the serratus anterior to achieve optimal scapular movement during throwing. Oftentimes the upper trap is over developed or over activated, throwing off the normalized force couple ratio.

Lower Trapezius: The lower fibers of the trapezius muscle, located in the middle and lower back region, act as a downward rotator and depressor of the scapula. However, during throwing, the lower trapezius also provides a stabilizing force to counteract excessive scapular elevation. It helps maintain proper scapular position and control, preventing unwanted elevation and allowing for smooth and efficient upward rotation.

Together, the serratus anterior, upper trapezius, and lower trapezius form a force couple by coordinating their actions to produce upward rotation of the scapula during the throwing motion. This force couple ensures optimal alignment and stability of the shoulder joint, allowing for efficient transfer of forces from the lower body and core through the scapula to the humerus. The proper function of this force couple is essential for generating power and speed in throwing while minimizing the risk of injury.

Thoracic Spine Mobility: The ability to rotate and extend the thoracic spine is essential for generating optimal shoulder mobility, allowing full scapular movement and adding to the power in throwing. Adequate thoracic spine mobility allows for proper positioning of the scapula, facilitating smooth movement and reducing excessive stress on the shoulder joint. Insufficient thoracic spine mobility can limit the range of motion in the shoulder and force compensatory movements in other areas, potentially leading to decreased throwing performance and increased injury risk.


In summary, the shoulder blade (scapula), spine, and rib cage all contribute to the arthrokinematics and kinematics of shoulder motion. Proper scapular coupling ensures stability and alignment of the shoulder joint, while thoracic spine mobility allows for optimal scapular positioning and coordinated movement. In high-level throwing, such as playing quarterback, these factors are crucial for maximizing throwing performance, minimizing injury risk, and maintaining overall shoulder health.

  1. Focus on serratus strength and activation always
  2. Include Lower Trap exercises with less upper trap MVIC to rebalance the couple (ie. prone cobra)
  3. Promote Thoracic rotation, extension and flexion in a multitude of exercises during the week
  4. Allow for a free scap in almost all exercises to cleanly upwardly rotated and glide along the rib cage
  5. Limit exercises that have prolonged scapular retraction or pin the scap back for under load
  6. If scap are bound into retraction on an exercise include a super set with scapular mobility exercise and T-Spine movement