Any good instructor will tell you that in order for martial arts to be effective you have to be in good shape, technique alone will not make you effective.
That's odd. I consdier myself a resaonably good instructor. And while I will agree that conditioning is a generally good thing for life in general, it is certainly NOT mandatory to be effective at defending yourself.
I'm not in anything like the condition I wish I was, but it's been less than an hour since I put a person (who I doubt has any actual training other than as a badass gangbanger) half my age on the ground, tied up in a knot, till Security could arrive.