Greetings.
As I mentioned before, for keeping a stable structure while retreating or stepping back that can withstand load, certain movements (Alignment Mechanisms) have to be executed. This way, you can strike or withstand pressure effectively even while yielding space, which can happen, and must be prepared for.
As mook jong man said, this is not trivial and it is not common knowledge. I can show this easily yet it is hard to write about because of the lack of uniformity in postures and stances and their names and execution.
So I will propose an experiment. It is a comparative experiment in which you will notice the difference in load capacity of your stance/posture (by the steady pushing of a study partner against your shoulders to test your posture stability).
For lack of uniformity, take a forward facing stance that you would use for striking, not a YGKYM. The one that looks like a T stance yet your feet are in two "lanes", not one in front of the other.
Now notice how stable the stance is by having a study partner push you. You should be able to hold the pressure without collapsing. If you collapse under the pressure, then ask for the experiments to develop systematically a stance that does not yield... that way your striking should have lotsa more power if you have this posture at the time of impact.
Onwards.
Now step back a certain way, step through, push-drag reverse, etc. After each, notice the posture you end up with, and test for stability. Notice if it is better, the same or less stable.
Now, do the stepping back again, yet after stepping back, "stomp" your front foot immediately after the back foot plants. Now test for stability. Notice if it is better, the same of less stable.
Now test with different ways of stepping back. Then report. Have fun!
Juan Mercado
from the labs of Martial Science University - Puerto Rico campus
Academia de Artes Marciales de Carolina