Mobility VS Isolation

Mobility: the quality of being mobile.
Mobile: capable of moving or being moved readily

Isolation: an act or instance of isolating.
Isolate: to set or place apart; detach or separate as to be alone
( www.dictionary.com )

When you are in the gym, look around you. You’ll find machines and lead weights, balls and bands, steps, slides, and stretch mats. Each one of these items was designed to utilize a certain function of your body. Your body, however, was not designed to work within the confines of a certain function. Your body has many functions, and unless you consciously tell it otherwise, it will perform any action it feels necessary to generate your desired end result. If you want to pick up a glass, for instance, your brain says “pick up glass”. Your body responds by activating muscles in your shoulder, arm, hands and even back to accomplish the end result, “pick up glass”.
In other words, your body does not isolate any one part of your musculature. It will not send signals to your muscles in order. When you think “pick up glass”, your brain doesn’t respond by saying,

“OK, shoulder, you contract first to lift the arm, now arm ... you bend to put hand to the glass, and hand when shoulder and arm are finished I want you to bend the fingers and grip the glass. Now everybody hold on while the shoulder lifts more to pick up the glass ... good job everyone!”

Instead, the signal “pick up glass” is sent to all muscles at once, and your muscles in turn send constant and unconscious signal feedback - not only to your brain, but also to your spinal column - which returns the signal in an order that accomplishes the original order to pick up a glass.
So if your body doesn’t isolate, why are all those machines and other tools in the gym designed to isolate? Weight machines and particular weight lifting techniques were not designed by doctors, anatomists, or physiologists, they were designed by athletes - a particular type of athlete called a weight lifter or body builder. Almost everything we know to do in a gym is designed for the particular athletic goal of weight lifting or body building/sculpting.
Now you have to ask yourself, “Am I or do I want to be a weight lifter or body builder?” If the answer is no then you shouldn’t be isolating your body the way a weight lifter or body builder does. You can, however, use the tools of a body builder or weight lifter to improve the movements you want your body to accomplish like carrying heavy groceries or climbing a ladder or even pushing a car out of the snow. Pushing a car out of snow is not a mobility inhibiting motion, so neither should your training be.
Try to imagine health or fitness and body building/weight lifting as unrelated pursuits with common materials. Similarly think of a newspaper. A newspaper is most commonly used for reading, but it can also be used to start a fire, insulate packaging, or swat a fly. If you want to swat a fly, you’re not going to sit and read the paper the way it was originally intended to be used hoping that the act of reading will somehow nab that pesky fly. Rather you will roll up that paper and swing it around like mad - a use totally unrelated to reading - until you accomplish your goal. The same is true for the materials in a fitness gym. If you don’t want to be a body builder/weight lifter, don’t use the fitness club materials exactly as a body builder/weight lifter would.
If you do want to be a body builder, or even if you just want to build your body for beach season, there is no reason you can’t do the exercises designed by these athletes to accomplish such ends. There is nothing wrong with isolation exercises and in point of fact much study and many years of practical application has lead these athletes to excel in their profession, but what they do is no more applicable to everyone else than is shooting a basketball or learning to crochet. You just have to understand that by using isolated movements, you are sacrificing mobility one way or another and in order to maintain proper range of motion you will need to practice mobility separate from your isolation exercises.