In The Natural Method, especially in the second book where it is outlined, Georges Hébert lists the benefits as follows (excerpt):

 “MAIN BENEFITS OF THE FUNDAMENTAL ARM POSITIONS

The fundamental arm positions produce the same benefits/effects as the Upright Stance, but with greater intensity when it comes to stabilization of the shoulders backwards and the shortening of the muscles that bring the shoulder blades together.

The movement of “hands at neck” also acts very energetically on the realigning of the cervical curve.

Note: The fundamental arm positions, when executed dynamically (as movements) can be either performed in place, or preferably while walking/marching.”

Additionally, and I invite you to experiment this yourself, each position affects not only your posture, but your leverage and how you “top load” the body. An easy way to understand that concept is by taking a popular exercise like the Squat and go through the variations of how we load the body with weight and where:

• Barbell Back Squat.
• Barbell Front Squat.
• Zercher Barbell Squat.

I am not of course discussing kettlebell goblet squat or double kettlebell front squat, or using a sand bag for the same moves (which is well-taught in Josh Henkin’s DVRT system, or Dynamic Variable Resistance Training), rather discussing the placement of the load in these variations and how the same weight may feel heavier or lighter from one variation to the next.

Try even something simple like some sit-ups with your feet anchored to a stall bar’s bottom rung or with a partner holding your ankles (and try that Janda-style too!) and let me know how that feels!