To engage in an intense exercise or fitness regime which causes one to ignore relationships and responsibilities; usually a short-lived affair seen at the beginning of the year and immediately prior to bikini season.
Jessica: "Sorry I didn't call you back. I was on the treadmill. I love the way I feel now that I'm losing weight!"
Martin: "Well, I swear to God, if you don't answer the phone again because you're stairmasterbating I'm going to come over and poke Rocky Road down your throat."
Martin: "Well, I swear to God, if you don't answer the phone again because you're stairmasterbating I'm going to come over and poke Rocky Road down your throat."
by vaguelyethnic March 29, 2010
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