Ask a PT Response: "While it is impossible to diagnose the cause of your pain without more information and a proper evaluation, based on your description, a few general conditions may explain the pain you are experiencing.  The first is a muscle strain or tear. This occurs when the force applied to the muscle exceeds its ability to absorb or stretch upon impact.  This can accumulate through minor repeated stresses over time, or as the result of a single event.  The calf muscles play a primary role in walking, running, and climbing steps by helping to propel an individual. If these muscles are strained or torn, they will be very painful when stretched and when actively contracting. This is a reasonable explanation for your pain, specifically with increased symptoms during activity that subsides during rest. 

An alternative explanation is tendonitis.  This is inflammation that can occur in any tendon (the end that connects muscle to bone), but specifically the calf muscles and other smaller muscles that aid its function. This condition will present with similar findings as a muscle strain or tear, but symptoms may be more localized to the insertion sites of the muscles (tendon).   

Thirdly, it is possible that what has occurred is a stress fracture. This is an injury that occurs in the bone due to repetitive stresses over time, in which the bones repair mechanism is slower than the damage that occurs.  Activity will usually exacerbate this condition, while rest will usually decrease its symptoms.

Certainly there are other possibilities, however, the these are common injuries that occur in the region you are describing.  It is important to consult your physician or a licensed PT for a proper evaluation and proper treatment for your pain."