I run approx 30-40 miles a week. Mostly on flat roads but recently in preparing for a 50k I have been running out in Long Island where it seems all the roads are rolling with plenty of good hills. On my left leg just below my calf and just above my Achilles I have been troubled with a very sore to the touch tendon. It's fine when I start out but becomes quite painful after 5-8 miles. Is this something I should try and strengthen an train thru or should I leave it alone for awhile. Any educated/experienced answers appreciated. Thanks.