sore abs, anyone?

Yesterday at the gym I did this:

.25 mile run on treadmill
50 squats
50 sit-ups
.25 mile run
50 squats
50 sit-ups
.25 mile run
50 squats
50 sit-ups
.25 mile run
50 squats
50 sit-ups

My abs hurt today. I was supposed to go today as well, since my trainer is going to be out of town the rest of the week...but I didn't plan on 2 ft. of snow falling last night. *sigh*