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1.
The acronym for it's Still Yo Mother Fuckin' Set.

A term used bodybuilders and weightlifters alike indicating you have not completed a repetition for a particular workout.
Guy 1: My girl just called. I gotta be outta here.

Guy 2: You cannot leave just yet. ISYMFS
by jasonthecancer March 09, 2014

Words related to isymfs

fitness focus push yourself work
 
2.
It's Still Your Mother Fucking Set

A common saying by pro-bodybuilder Ronnie Coleman
Person 1: I really want to lift more weight, but I can't

Person 2: Then go lift more weight! ISYMFS
by iliftweights September 11, 2013