A weak diaphragm (= high position of the diaphragm) will bring the thoracic spine in flexion (kyphosis).

This increased kyphosis will bring not only the lumbar spine in more lordosis but also the cervical spine.

With the cervical spine in more lordosis (extension) there is more load of the head on the facets and this extra compression can cause inflammation.

And as we know, the facet joints are the main threat to the nerve roots.