Heh, the P90X has a section on this that's quote worthy:
Often, you will hear the expression "No pain, no gain" when it comes to achieving fitness results. Understand that this does not refer to the kind of pain that a trapeze artist would experience after missing the net. What it does refer to is muscle burn that is common during intense workouts. It's a GOOD pain. Let's review: missing-the-net pain, bad; muscle-burn pain during intense exercise, good!
Okay. the highlighted portion makes me giggle.
Sandpaper occurs a few seconds after beginning running. I think this means that I shouldn't run during my all-year allergy season.
-Carefully taking sips from the Fire Hose of Knowledge