Lately I have been running with a new thorn in my side...my heel. Usually it's my knee or lower back but the last few times I have gone out for a run, my left heel has been hurting. A lot. I knew enough to determine that my achilles tendon was the culprit but I decided to do some research to see what would cause it. I found that not only does soreness and pain occur in the achilles, but it is something common to runners. Go figure.