The majority of people I meet interpret the instruction to stand up straight by lifting the front of the rib cage up and taking the shoulders backwards. I wonder where this began because from where I stand and teach absolutely no good comes from an elevation of the front of the ribcage.
It might seem counter intuitive but one of my main instructions, or wishes, is for the back of the body to lengthen in order to let the front of the body soften. From my perspective everyone is too long in the front of the body and too short in the back. This goes for the whole system but I tend to focus most on the space between the pelvis and the ribcage where this imbalance wreaks its greatest havoc.
When I begin my yoga classes I often start with a rap about lengthening the back of the spine to soften the front of the body. I think this is an interesting image. If I get proper extension at the back, the overextending front should release or shorten a little. Lengthening the back of the spine skyward should release tension at the front of the throat and ease the front of the ribcage downwards a bit freeing up access to a much deeper breath.
The idea of standing up straight implies a structure that would be equally straight at the front and its back. If you believe me that we tend to be tighter in the back of the body than the front it would make sense that finding even balance in extension would be difficult.
If you shorten the front without lengthening the back it is easy to create unwanted compression in the cavities of the trunk. Lengthening the back muscles is likely more difficult than shortening the muscles of the front which makes it a complicated project.
Softening the front of the ribcage is a project well worth undertaking but not a no-brainer. Bringing balance to a dynamic machine requires a conscious effort.