The first one of these is An example of how important your sleep positioning can be. In that I cover the similarities between a lateral pelvic tilt and how one sleeps. Next up, the similarities between sleep positioning and a swayback posture.
First up, going over a swayback posture. I’ll use some pictures from Kendall’s book, many of which are found online.
The most pressing aspects of this posture are:
The hips are extended:
The lower back is being pushed forward:
Often to the point it’s in extension:
The thoracic spine may be flexed, and head in forward head posture:
Note how far the head is in front of the shoulders
From the side, we could simply say the body’s center of mass is being pushed forward:
With that, it’s very common for the feet to be turned out and or the knees to be turned in. (This isn’t so much part of being a “swayback” as it is common postural / movement issues.)
And the neck may be tilted,
These are very, very common issues.
–
Connection to sleep positioning
Let’s look at someone sleeping on their stomach:
Right away, there’s some obvious connection. The lower back is extended:
The hips may or may not be extended.
This can depend on the mattress’ hardness. Here’s a good picture from a mattress company:
Specifically looking at stomach sleeping:
Notice in the “Soft” category the hips are extended:
Because the body’s center of mass is located around the hips, this is where the body is most likely to sink into the mattress.
Even if you’re on a hard mattress, negative things can happen at the hips. Because gravity is still acting on the hips, gravity can still push the head of the femoral head downwards:
I’ve written about this hip ailment before here, here, and here. In summary, it’s not a good thing.
A less obvious connection is at the feet. When sleeping on the stomach it’s very likely the feet are going to turn out:
Finally, the neck. It’s typical to favor having the head turned one direction more than the other. I haven’t really examined this, but it seems most people favor turning their head to the left. Even a quick google image search of “Stomach Sleeping” seems to agree:
Of the people on their stomach, notice how many have their head to the left.
This coincides with what you often see at the neck in stance: Tilting to the left.
–
A full comparison
Our two positions:
Outlining:
Rotating:
The other way:
Get off your stomach.
–
You can get my manual on sleep positions here: 
Or find more about it here.
–