Posterior Tibial Tendonitis. Likely caused by overpronation of the foot. Pain is noticeable around the arch, and sometimes also on the outside top of foot opposite the arch. First noticed the week after Seven Hills Run. Got better with rest, but has resurfaced once I started running again.
This is a mild case only. Perhaps my gait has changed, or that the cushioning in the shoe has deteriorated.
Recommended treatment: ice, aleve, and new insoles with better arch support. Also maybe a new pair of shoes. Oh yeah, no barefoot walking.
There hasn't been any pain post-run in the last week. More importantly, no discomfort felt after the hard hill repeats yesterday. So I'm going to take this off the list.
What helped? New shoes, or more specifically not wearing the Pearl Izumi. No track/super fast running plus icing also helped. I've also done a much better job stretching.