Yesterday, my abs were sore all day. It wasn't like it was killing me, but it was really annoying and distracting. I was also so tired all day.
I did the next run on my training schedule, which was 50 min with 4 - 6 60-s hard intervals. I ran on the treadmill starting at 5.8 mph and increasing to 6.2 mph so that the average of my "easy" pace was 6.0 mph. I did 5 60-s intervals at 7.5 mph. This was a hard run, since I was just so tired. My abs didn't really hurt more during the run, but I'm sure it affected me. I took a lot of breaks.
Fortunately this morning my abs started to feel better. I could still feel some soreness, but not nearly as bad. I still don't know what the problem was!
This morning I went to my usual boxing class. I was still tired, but it went OK.