I had a nice conversation the other day with a good friend about the current anti-isolation trend in "functional" training. He mentioned that he was recently TOLD by a gym member that there was no reason to ever do isolation work - that compound movements were all anyone ever needed. ...sigh... As with many of these things, (like stretching, isometrics, partials, eccentrics, etc) we need to be careful not to throw the baby out with the bathwater, because there really is a precious baby in there.
Isolation exercises are extremely "functional" for the following:
When I was 18, I read (I think it was) an Arthur Jones quote that went something like "You want big arms? Train until you can bench 500, rows with 300, and do dips and chins with 100lbs strapped around your waist, and you'll have 'em!" I took that to heart and cranked out the dips and chins, benches and rows. No matter how much I gained in those exercises, it always seemed like the tank-top guy over there cranking out the curls and triceps extensions had better arm development... Bodybuilders get it. Men's Health guy gets it. Why don't the rest of us?
I shouldn't need to expand on this here - it should be obvious. If a person is suffering from injury, isolation work may be key. As a tool to stress and strengthen specific areas without unnecessarily stressing areas that need rest, what else is there? Yes, squats, pulls, and hill running will strengthen the posterior chain from the Achilles tendon to your iliocostalis, but are they your best options for someone regaining ankle and knee kinesthetic awareness, mobility, and strength? Probably NOT.
Consider a powerlifter who has just finished doing uber-tons of squats and pulls. If he needs to do some work for his VMO to maintain proper knee health, should he load up the barbell and crank out some close stance front squats, or would he be better off doing some backwards sled dragging, terminal knee extensions, or [EGADS!] some leg extensions? The correct answer would generally NOT be to add front squats unless this powerlifter has a goal of running himself into the ground with auxiliary lifts. Isolation will give the trainee a chance to bring up specific weaknesses with minimal inroads into recovery.