The instructor for my core and weights class didn't show up this morning at 5:30 , so I headed to the treadmill (dumb, since I have one at home). I was able to do 4 running intervals of 1-2 minutes for a total of 22 minutes without my foot hurting. It's a little tender now, but not like before.
I wonder if the difference is that I was wearing my"aerobics" shoes which have a much more cushioned heel.
We'll see how my foot feels later today.