A.  Pain in the lower leg of an avid runner who runs few miles everyday can be due to medial tibial stress syndrome. X-rays are usually normal and an MRI can only diagnose this by seeing the marrow oedema. I would advise you to get an MRI of the leg to look for this condition. Usually " relative rest" is the treatment, which means cutting back 50% of the running miles for next few weeks.

Continuing to run in this condition despite pain can lead to stress fracture.