Thanks, Lol. I really was not happy about dropping out of the race, but I could hardly walk on Saturday. My foot really got swollen, so I wrapped it and elevated it as much as I could. The swelling is down, but the pain isn't quite gone yet. As such, I'm going to hold off on anything lower body for at least a week, maybe more if I find out that the sprain is really a break.
I'm truly not sure what caused the injury - could have been most anything, really. I'm not blaming the Vibrams; I've run too much in them without incident to suspect them as the cause. I wish I knew what caused it though!
In terms of the run intervals - do them without a break. Using my previous example....
For run 1 (1 mile), warm up with a slower pace for a quarter mile, speed to a comfortable pace for about a half mile, and then up the pace steadily through the last quarter mile. Walk for as long as you need afterward to bring your heart rate down slowly.
For run 2 (1.5 miles) do the same quarter mile slower pace warmup, speed to your quicker jog for a mile, then up the pace through the last quarter mile.
What you want to be able to do is recognize the changes in your heart rate and breath through the run, so you'll know how much you can push (when necessary) while avoiding walking later in the run as a result. As you increase the distance, try to do mini pace increases once you are warmed up and comfortably into the run. As an example, on a 5 mile run, warm up the first quarter mile, adjust to your jog pace, and then anytime after the first mile, do little bursts of speed and then return to your comfortable jog. Really push the tempo at the end of the run for a quarter mile to empty the tank, and your overall run endurance will skyrocket. As an added bonus, you'll know how much you can push intra-race without completely burning out halfway through.
Training for me now returns to the land of triples, with a few add ons here or there. The schedule is going to be a bit nutty, but my intention is to do triples work through the end of the year and then re-evaluate. Bench and standing press sets should happen tonight, with some core work in the middle to start to prepare for lower body strength work again.