ART= ACTIVE RELEASE TECHNIQUE (or thereapy. I always mess that one up).

I believe that it's kinda like a deep tissue massage type thing that loosens up the fascia that get's tight from the heavy loads that come with a heavy training schedule.

I've had ART guys work on me during IM training when my muscles get "loaded up" with junk and MAN does it loosen me up and make me feel better.
In the later parts of my heavy training periods I always notice that I feel heavy and my muscles almost feel like they are ready to snap. I also start getting niggles of pain here and there. That's my cue to call my ART guy.