I listened to a recent webcast from Dr. Shirley Sahrmann in which she says a if you can't recruit a specific muscle under a controlled condition, there is little chance it will be beneficial in an integrated manner. If you read her "movement impairment syndromes" book, a lot of open chain strengthening done on-table with alot of grooving movement patterns to get that muscle working in the real world sort of speak.
Dr. Eyal Lederman, on page 10 of his "Neuromuscular Rehabilitation in Manual & Physical Therapies" he says, "There are several misconceptions about motor control which are likely to make rehabilitation unnecessarily long and complex. They all originate from the principle of "isolate in order to integrate". The muscle is NEVER the goal of the movement. Focusing on tensing, clenching, bracing, or holding specific muscles during movement turns them into the goal of the movement. Muscles work in complex synergies- they never work alone. All muscles are equally important, even muscles that are silent. Muscles which are slow or at low EMG activity are part of the whole control pattern."
Sahrmann's approach is very much, "isolate to integrate".
In her excellent text, "Diagnosis & Treatment of Movement Impairment Syndromes", for the most part she uses very isolated corrective muscle work. On page 32 she says, "the desired muscle action should be practiced under the specific conditions in which it is to be used."