How to tell if i cracked a rib, or just injured a muscle in center of mid back, below shoulder blades? pain when bending but not if stationary.

Either: Both cracked rib or muscle pain hurts with movement but fine if still. No tx for cracked rib, so Motrin and muscle spasm meds , ice early, heat later and some time , 6-8 weeks.

Get an x-ray: An x-ray would be necessary to diagnose a fractured rib. Usually a fractured rib would be painful with movement, deep breathing or coughing. It would also be tender on feeling it. The center of the back would be an unusual location for a rib fracture--it should be off to one side or the other.