Specific Adaptation to Imposed Demand (also known as Specificity)
in a nutshell this means that you will adapt to / get better at whatever you do. This is just how the human body works. Its not a suggestion but a law.
Evidence from neuroscience goes a step further saying that we are always adapting to our environment, in fact we adapt to everything we go through in our daily lives. How we adapt is by making the next time we do these particular activities a little easier. This means we are always trying to figure out ways to spend lass energy – which is good for survival but not ideal for our posture in todays society!
The S.A.I.D Principle does NOT necessitate that doing corrective exercises will magically fix your movement dysfunction. Glute Bridges will not necessarily make your squat better. Doing glute bridges will get you better at doing glute bridges only.
How Corrective Exercises Work:
A corrective exercise like the glute bridge works through understanding WHY you are doing them and how they feel, and then being able to apply that feeling into your squat.
A corrective exercise is a solution to a movement problem. Proprioception (or how your body feels) is how your transfer your glute bridge skill into your squat skill.
The S.A.I.D Principle is why in the gym you train fundamental movement patterns like the squat, deadlift, pull up and push ups etc. We always want to be perfecting these fundamental movements that are the basis for all the rest of human movement. The best athletes practice basic drills to perfection, so should you.