There are three muscles on the inside of the shin. Two which curl the toes down, Flexor Digitorum and Hallucis Longus, and Tibialis Posterior which turns the foot in, or most importantly, controls pronation or foot roll and decelerates impact when running.
These can all become stressed, inflamed, strained and torn. The pain is often felt on the inside of the shin at various points and is usually worse when using it. Most muscle pain is comfortable at rest.
The causes are usually overload due to errors in how you use the foot and ankle when running. Treatment to assist the healing process is always complimented by work to alter poor bio mechanics and sort out the reasons why the muscles have become injured. This is what Physios do!