Category: 3DMAPS
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Crosbie J, Kilbreath SL, Hollman L, York S. Scapulohumeral rhythm and associated spinal motion. Clinical Biomechanics 2008; 223: 184-192.

The purpose of this study was to describe the kinematic relationships between the humerus, scapula, and thoracolumbar spine when raising the arm overhead. The 32 female subjects performed unilateral and bilateral arm elevations while sitting. The arm(s) elevation occurred in the sagittal plane, frontal plane, and in the plane of the scapula (30 degrees forward of the frontal plane). An electromagnetic tracking system was used to detect the three-dimensional motion of the bones.

The authors’ findings were consistent with similar studies that demonstrate consistent motion at the scapulothoracic joint and in the thoracic spine that is an essential component of arm movements. Interestingly, there was substantial upward rotation of the scapula (frontal plane) and external rotation of the scapula (transverse plane) during both unilateral and bilateral shoulder flexion (sagittal plane). This “speaks” to the Applied Functional Science® (AFS) Principle of 3-D; specifically, the fact that motion in one plane can’t be totally separated from motions in the other two planes.

The study also documents, as would be expected, that thoracic motion was reduced with bilateral arm elevations compared to unilateral arm elevations. The Chain Reaction® motion of the thorax facilitates unilateral arm motions. However, with bilateral arm movements, the thoracic motion that would facilitate one arm would inhibit the other arm. Therefore the bilateral arm movements “cancel” the thoracic contributions except for sagittal plane extension.

For practitioners of AFS, the strategy of improving thoracic and scapulothoracic motion in order to protect the shoulder joint from injury and improve arm function is supported by this study. The rest of this blog and the video linked to it will focus on Strategies derived by “reversing” the Chain Reaction®. Dr. Gary Gray has described a progression of task-driven arm movements to improve position and movement of the thoracic spine. The problem of thoracic kyphosis (slouched posture) will be used as the example condition to be addressed.

When a patient / client sits or stands with a kyphotic position of the thoracic spine, he / she is often instructed to “sit or stand up straight.” The person may be able to consciously hold this position for a few seconds, but once his / her attention moves to other things the conscious “hold” is lost. The AFS Strategy would be to take advantage of the Principles of 3-D, Chain Reaction®, and Load to Explode. The Strategy would save the unsuccessful sagittal plane until last. The desired spine extension (explode) would be achieved by loading in the opposite direction first. 

Using unilateral arm reaches in the frontal plane, the reach in the load direction turns on the muscles to create the opposite motion. Reaching down followed by the explode up in the frontal plane (shoulder adduction to abduction) will contain thoracic extension as documented in this research cited above. The direction of the reach would be progressed forward from the frontal plane. As the target of the reach moves forward, more transverse and sagittal plane motion of the arm, scapula, and the thoracic spine occur. The focus of the motion can be shifted to the “explode” up. The position of the target for the reach can be tweaked to increase the height, thereby moving the load and explode more towards thoracic extension. Finally, the reaching can be transitioned from unilateral to bilateral, which will force the thoracic spine motion to be primarily extension as documented in this research.

The goal, through the loading to exploding strategy, is to turn on and strengthen the muscles for thoracic extension. Doing this subconsciously via the proprioceptors using a task-driven movement improves the chances that the position of the spine at rest will be less flexed and the motion more functional!

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Evidence that Matters for Function: Leveraging Arm – Thoracic Spine Chain Reactions – Vlog

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