Spry Juncture, LLC
How to Evolve Gracefully
Serratus Posterior Inferior
Region
Origin & Insertion
['Origin: Spinous processes of T11–L2', 'Insertion: Inferior borders of ribs 9–12']
Synergistic Muscles
['Internal intercostals', 'Latissimus dorsi']
Joints
['Costovertebral joints']
Primary Actions
['Depresses lower ribs (9–12) during exhalation']
Nerve & Spinal Segment
Ventral rami of T9–T12 spinal nerves
Thoracic spinal nerves; no plexus
Interesting
Considered a transitional respiratory/postural muscle. [Netter's]
Reversal of Action
Anchor ribs to lift spine during spinal extension
Common Dysfunctions
Restricted breathing, thoracolumbar junction pain
How to Stretch
Deep exhale with forward bend or foam roller.
Trigger Points
How to Strengthen
Resisted exhalation drills or deep core engagement.
Concentric Action
Depress lower ribs during forced exhale
Applications:
Used in breathing pattern retraining and trunk stabilization
Eccentric Action
Control rib movement on inhalation
Isotonic Action
Deep breathing with resisted exhale
Related Conditions
['Thoracic spine restriction', 'Postural fatigue']
Isometric Action
Maintain rib depression during core bracing
Exercise Ideas
['Prone press-up with exhale', 'Breath-focused planks', 'Foam roll reach & breathe']