For the TL;DR folks, the short version of running with Achilles tendonitis:
60 minutes at marathon pace+25 seconds per km, 3x/week, is way too much. 20 minutes (inspired by Charlie) at MP+1:25/km is fine, can be done every day if desired. Not much fitness going on though. 45 minutes at MP+0:45/km seems to be the sweet spot, with current injury status can be done two days in a row, but not three.
If you care to read the long version....
A quick recap of how I arrived where I am:
When I sprained my ankle in October, two weeks out from my half marathon, I took a whopping three days off, tested the ankle with some shorter runs, and ran pretty well in the half -- just 3 minutes slower than my PR. Buoyed by this apparent success, I jumped right into training for the spring full. The hillwork went okay, but trying to transition to long intervals the ankle worsened so I had to stop those. I ran the full in a PR time, took a week off afterwards, and began gradually adding volume again -- which is when my real troubles began.
With the low volume I allowed myself too many strides on short runs, too much running on grass, too much sprinting up little hills, and I threw some short races in there as well. A month like that and the word I was using to describe my heel was "spongy". It was really just a kind of generalized morning fire from the bottom of the heel all the way to the back. A combination of plantar fasciitis and Achilles tendinitis. I came to my senses and was already somewhat rehabbing the ankle before I went on vacation, where I delivered the one-two-three combination that knocked me out: (1) Sunday I did a 45-minute run on soft sand/loose gravel, which left me limping badly on Monday morning. (2) Monday afternoon the youngsters were having fun -- sprint down the wooden dock and leap for distance into the water. I joined in the game and immediately came up hobbling on the first sprint. (For dignity's sake I did "finish the race" with a leap at the end.) (3) Tuesday afternoon wading around in the falls I stumbled and whacked my left heel hard against a boulder. I'm actually proud of myself that I did not scream or cry that time.
Just like Achilles of the epic, my very existence had narrowed down to a single tendon (and attachment). After the own hat trick, rehab began in earnest, beginning with time off for the pain to subside. It was actually an easy decision since vacationing in paradise I had hiking, swimming and walking available to me. I took nine days off from running.
To run, or not to run -- that is the question:
Not running was clearly working, so there is that. But I believe in attempting the MAXIMUM effort while injured that still allows the injury to improve. (The reasons why I believe that are complicated, suffice to say that I have put a lot of thought into it.) So I have been running, playing around with different distances and intensities (nothing much longer than an hour, nothing much faster than marathon pace), results given at the top. I did completely clear my fall race calendar, next race will be a 5K on 1/1/2014, fingers crossed.
How I define "too much" is not based on how the ankle feels one day to the next. I take a longer view and base "too much" on how the ankle feels one week to the next. For example, if I run 3x/week 60 minutes at MP+0:25/km, two weeks in a row, how does the ankle feel each morning the second week compared to the same day the previous week? If it's not better, week over week, most of those days, then that's too much running. It WAS too much running, so I adjusted way down.
By contrast, "too little" CAN be evaluated one day to the next. I wouldn't expect running to have the same benign effect as a day off, if it does then it was probably "too little". Just repeat the same run a few days in a row and it quickly becomes clear that it WAS too little. So I adjusted back up.
So, my personal conclusion is that it is possible to run with Achilles tendinitis and still have it improve, provided I also do some other things. Like stretching, which I will write about next time.