04/29/2026
Neck and shoulder pain isn’t always a local tissue issue.
The phrenic nerve originates from C3–C5 and provides motor and sensory innervation to the diaphragm. Sensory fibers also carry input from surrounding structures, including diaphragmatic pleura and peritoneum.
When the diaphragm becomes restricted or irritated (e.g., altered breathing mechanics, increased intra-abdominal pressure, or local inflammatory/lymphatic congestion near the liver), afferent signaling through the phrenic nerve can increase.
Because these signals enter the spinal cord at C3–C5, the brain may interpret the source as somatic structures in the same segmental region- commonly the upper trapezius, levator scapulae, or shoulder tip. This is a classic example of viscerosomatic referral.
Additionally:
* Reduced diaphragm excursion → decreased lymphatic and venous return (the diaphragm acts as a mechanical pump)
* Increased fascial tension → altered rib and thoracic mechanics
* Heightened sympathetic tone → increased nociceptive sensitivity
This creates a feedback loop of:
restricted diaphragm → altered neural input → perceived neck/shoulder pain → further guarding
Interventions that improve:
* Thoracic and rib mobility
* Diaphragm function (breathing mechanics)
* Nervous system regulation
…can reduce aberrant input and improve symptoms- even when the pain presents in the neck or shoulder.