This is a quote of a quote that I read in a really great synopsis about PNF. PNF: A Technique or System.
"Newer vies of synergies are saying that a muscle can belong to multiple synergies; in addition, an individual muscle has a unique contribution to each synergy. Finally, the total activation of a muscle is dependent on both the simultaneous activation of multiple synergies contaning that muscle and the relative contribution of that muscle within each of these synergies."
Shumway-Cook and Woollacott 2012.
In other words, think in movements not muscles. Your brain is going to get movement somehow. Isolationism can have it's place in a return to "finding" the muscle, but I think must quickly progress into using the "Muscle" in multiple planes of motions, under multiple types of loading patterns.