TVA and Drawing In Your Abdominals while Squatting

This is the original question posed to me which prompted this article;
I am a novice powerlifter and I train and compete raw (no wraps, no suits,
no belt) and I was wondering what I should be doing with my abs during the
squat. Should I be sucking them in, or pushing them out, or something else
altogether? Does the same apply to the deadlift and bench? Note that, I hold
my breath throughout most of the lift(s). I begin to exhale after the
sticking point. Will this have any bearing on how I should use my abs? >>

*** What you appear to have been doing intuitively is most appropriate.
Breath holding is a reflex action meant to stabilise the body or to enable it
to produce maximal force or power under heavily loaded or suddenly imposed
stress.

There have been numerous claims that sucking in the abs or deliberately
trying to activate the transversus abdominis (TA) muscle is the best way of
stabilising the trunk during all activities. While one can voluntarily
control muscles during the initial phases of an exercise or during very slow
manoeuvres, it is not possible to do so under dynamic conditions, such as
encountered in the later stages of lifting or in any complex sporting
actions. In fact, any attempts to do so may profoundly disrupt your movement
patterns, as has been pointed out for many years in the form of this aphorism:
‘paralysis by analysis’.

Another anatomical principle should be remembered in this regard, namely “The
body knows of movements not muscles”, so that any attempt to deliberately
alter patterns of muscle activation during dynamic movement in a person who
is not exhibiting any neuromuscular pathology may instill faulty patterns,
timings and rates of muscle synergism.

Note that all or most advice on ab ’sucking in’ and TA recruitment has been
extrapolated from the world of ‘average’ folk and not elite athletes, least
of all any type of competitive lifter, few or none of whom would ever
consider sucking in abs or trying to activate TA during the dynamic or
explosive phases of the lifts, because these unproven actions could cause
spinal injury.
Dr Mel Siff
Author of Supertraining + Facts and Fallacies of Fitness
http://www.drmelsiff.com