Delayed Onset Muscle Soreness

Well who knew?  Seems like everything's got a name...  This would explain those two painful days last week...

http://en.wikipedia.org/wiki/Delayed_onset_muscle_soreness

http://sportsmedicine.about.com/cs/injuries/a/doms.htm

http://www.webmd.com/fitness-exercise/guide/sore-muscles-keep-exercising