What are the causes of middle back pain?

Lots of things: Go see your physician first to make sure it isn't something scary. Then take a look at how you sit, your general conditioning, how you use your body. For help, try physical therapy to include mobilizations and increasing thoracic mobility, treatment by an osteopathic physician and a supervised stretching program. If these aren't helpful, sometimes it's from an old injury- physical or emotional.

Many: Back pain may be referred pain from pancreatic cancer, aortic aneurysms or dissection, metastatic disease of the vertebral bodies (bones) of the back, kidney stones( the scary diseases) . If there is history of i njuries then maybe related to vertebral compressions, disc bulgings or herniated discs (most common).

Muscular v disc: This could be muscular pain or related to underlying degenerative discs or even a herniated disc or other spine based conditions. Other issues could include referred pain from a lung or pulmonary issue or gastrointestinal issue like an esophagitis, ulcer, gallstones or reflux. Even a renal or kidney issue may be a cause. See your doctor if symptoms persist or worsen.