I am training for my first half marathon and am experiencing some pain in my knee, calf and heel. how do i know when to seek medical attention?

Can't run: Pain in these areas may mean your shoes are not supporting you. If it hurts or prevents you from running. It can be serious. You may see your foot specialist for orthotics or bio mechanical evaluation.

Severity of pain: Pain with increased activity can be multifactorial based on your general health, mechanics, shoe wear and training regimen. If your pain is more of an "ache" associating with increased mileage, altering your training regimen/shoe change, etc. May be satisfactory. More significant pain could signal a greater problem (stress fracture, etc.) and would best be evaluated by an orthopaedic surgeon.

Judgement: If this is the first time for this to occur, i would see either the podiatrist or the orthopaedic surgeon or both. Or, if available, a sports medicine md. This may be simple overuse - often when doing speedwork too much / too soon - but there are other causes. Check the wear on your shoes -- outside of heels. If heavily worn, could throw off your alignment. Good luck.