The problem with relying either on TA Isolation or bracing to protect your spine when moving under or with load is twofold. First, both encourage isolation of a specific group of muscles. And second, both call for "constant maintenance" by needing to statically hold an isometric position. Both these are an ineffective and time-consuming (especially in the long run) way of going about learning the mechanics of a motor pattern, weighted or otherwise.
Arguments against isolation
If we are smart enough to realize that a training program comprising of isolated movements only, is a thing of the past, Why do we continue to use "isolated control" (i.e. individual contraction) of body parts (motor units) when learning (or executing after having learned) a new compound lift?
If a movement is compound and functional, but to do that movement we end up having to isolate one component here and the other there, are we not in a way doing multiple isolated movements at the same time? Are we truly doing one compound movement?
And while setting up for a Snatch or a Clean, if you have to constantly rely on "cues" to "keep the back tight", "brace" your "abdominal wall", "shove knees back and out", "keep chest up" all the while anticipating future cues related to the impending second pull etc, are you really performing a Snatch? Are you not performing 10 different movements at the same time that will look like a Snatch?
The human body does not function as a group of multiple components working as a team. It is rather (and operates as) a single unit that is composed of multiple components. Why command the components separately when you ARE the unit?
Arguments against static/isometric hold
The idea and act of an "isometric hold" does not lend itself well to movement in general. Isometric holds (e.g. planks etc) are great to build isometric strength which most certainly will be of use when holding good positions during a loaded movement. But that does not mean, one should also do a "vertical plank" while squatting. When squatting one should just squat!
Ideally, while performing an activity the goal should be to minimize energy expenditure on anything else. This is true both for mental and physical energy. Isometric holds like TA contraction or bracing call for constant maintenance and active thinking during a movement, that defeats the very purpose of that movement. When moving (loaded or not) one shouldn't need to think!*
INTEGRATION is key
To move like they do, one must look at the whole picture. The three observations about the narrowness of lower abdomen, integrity and virtuosity/control, cannot be explained individually just how individual dots don't make sense by themselves. It is only when we connect them that we truly understand.
The fact is that these lifters' bodies are integrated. Their entire body is available at their command to move the way they are doing. They don't have the need for thinking about "elbows up" or any such cues.
They don't isolate or command individual motor units. They are the unit. They move.
Maybe some of you would argue that it is all about "practice". And that these athletes have essentially mastered true control by practicing their "technique" day and night to move like that!
To that I will say: Control or Technique is just a piece of the puzzle.
What use is either if they come at the price of constant maintenance? Would you rather not have such control and technique be the by-product?
Isn't that what true and unconscious Mastery is?
And what one should strive for?
Continued in part 5
Footnotes & References:
* This does not mean technique or cues are useless, as one has to actively think to use them properly. In fact, such thinking is crucial for a "late beginner". The argument is against using cues/thinking as a crutch and thus never striving for unconscious mastery of a movement. One way to such mastery is integration.