What's Actually Going On
A strength problem masquerading as a mobility problem
The thoracic spine (T1–T12) serves as the kinetic hub connecting the lumbopelvic complex below to the cervicoscapular region above — transferring loads across the entire trunk while protecting the heart and lungs. Hypomobility arises from two overlapping mechanisms:
Historical Explanation
Passive Restriction — Capsular tightening of facet joints and shortened posterior musculoligamentous tissues. Not the primary driver in most adults.
Dominant in Adults 40+
Neuromuscular Failure — Age-related motor neuron death causing sarcopenic weakness of erector spinae, multifidus, and scapular retractors. The spine locks into flexion as a protective strategy.
The Shoulder Link
Prerequisite
A minimum of 10–15° of active thoracic extension is required for the scapula to posteriorly tilt and upwardly rotate during arm elevation.
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Consequence of Deficit
Without adequate extension, the subacromial space narrows → rotator cuff impingement. Thoracic stiffness is not just a spinal problem — it is a shoulder function problem.
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Clinical Implication
Treating shoulder pain without addressing thoracic mobility is incomplete. Overhead volume must be reduced until ≥15° active extension is achieved.
