The Achilles tendon is placed under enormous strain while running, especially at higher speeds. Its also in a part of the body that doesn't have a good flow of blood, so any damage takes ages to repair. Thankfully, I have never actually ruptured my Achilles but I have had quite serious tendinitis (and more recently, a very mild case) in the tendons of my ankle. The good news is that now the problem seems to have gone away altogether, just in time for me to start running series today, in preparation for the 10k race I have on the 31st of December. In part, this is due to following the advice of a couple of Swedish researchers...
Apparently, one of them was trying to actually rupture his damaged Achilles tendon completely (all in the name of science, undoubtedly) by "eccentric loading of the calf muscle". Eccentric loading means to put a muscle under strain while it is contracting rather than stretching (concentric loading). What the researchers found and eventually demonstrated scientifically, was that the injury healed much more quickly when this routine was performed. In practice, you stand on the edge of a step and, using a hand to steady yourself, you lift yourself up on to tip toes using both legs and then lower yourself down to below the height of the step using only the bad leg. (If both of them are bad then I suppose you are screwed.) You do this a certain number of times each day - more details can be found here.
What I found perversely satisfying was that the recommendation was to add extra weights to the point of being slightly painful to complete the exercise. Is it just me or does it not feel as though you are getting better more quickly if the treatment hurts?
By the way, the condition used to be called Achilles tendinitis - the difference being that it was thought to be an inflammatory condition when in fact it is not. The point is that it is actually better not to take anti-inflammatories as a result. The reason the ankle feels stiff in the morning is because the collagen builds up in a random fashion around the damaged area; with use you break some of the structures leaving only the correctly aligned ones.
(DISCLAIMER: I am not a doctor or qualified to give advice on how to treat injuries. In other words, enter at your own risk, don't blame me, etc. Still, if there are any inaccuracies or things that I have simply got wrong, I would be interested to know about them.)