When I'm in a hurry, I tend to walk with my torso and head leaning slightly forward.
I see this in other people too. Leaning forward to reduce work is totally natural, but the way we lean is in part brought about by the muscular adaptations to our modern lifestyle (e.g. excessive sitting). So while trying to go fast or uphill would naturally create a forward lean, the ever-present forward lean (and the way we make it) isn't really natural.
If you saw someone (or yourself) walking like this, you might say "stand up straight, yo!" and then they (or you) would go like this:
But if we take a closer look, you'd find you still have your upper body out in front of the lower half (you're still leaning "geometrically"); all you've done is a backbend in the air to bring your head and shoulders up.
To correct the forward lean, there are different, hardly-used motions involved and a door jamb is the perfect place to practice them.
Put your body on a door-jamb grid (heels a couple inches away, with your butt on the doorway) and stand up straight. You might look like the photo above (where the entire torso is away from the jamb) or you might look like this:
where your head and shoulders are in line with your hips, but not your ribcage. Can you see how my mid-back (where the bra or HR monitor strap goes) is still thrusting forward away from the wall?
Guess what: The ribs have to be back too, otherwise you're still doing a slight version of a backbend--not great when you're applying 10,000 walking or running loads a day.
To take the backbend out of your spine, pull your ribs back to the wall.
You can slide the back of the head to the jamb as well--think "make a double chin--it's OK if your head doesn't touch.
Try this a few times until you have a sense of how to slide back to stack your parts upright, then try the old way of "aligning" your body (i.e. lifting and thrusting the chest and ribcage to bring the head up) again so you can feel the different.
Geometry is cool in that, sometimes to make a taller structure you have to go backwards in some places. While the backbend-method can bring your head and eyes level to the ground, it doesn't also bring your torso back over your body.
Note: The forward lean is like an orca's "floppy fin," readers of Move Your DNA. In most cases, your mid-back joints no longer articulate so try as you may, you're not going to get your head up AND your ribs back. The good news is, unlike the orca fin, this isn't permanent. You do need to learn this door jamb stabilization technique before you can mobilize though...and that's coming this month as well.
Note note: You don't have to walk around with your arms out in front of you unless you are a zombie. In that case, carry on.