The muscle that forms the anterior wall of the abdomen is called the rectus abdominus.
The quadratus lumborum is a fleshy muscule of the posterior abdominal wall that helps to maintain upright posture.
Quadratus Lumborum
gluteus maximus
The abdominal muscles do many things like hold and potect the abdominal cavity and assist in breathing. But, the most obvious one is posture. They are the antagonists to the muscles along the spine and help maintain spinal curvature. The action is known as flexion of the spinal column.
Your muscles will develop allowing you to maintain proper posture with less effort.
Erector spinae muscles
Upright Posture
an upright posture
yes
Erector Spinae. These muscles extend the spine and maintain the vertebral column in an erect posture.
Tonic contraction holds the muscles in position. In other words, muscle tone maintains posture.
These muscles are the core and they give proper posture to the body. That is they support the spine and maintain their optimal position and in turn helps in protecting the spine. for spine, maintaining proper posture is the best protection. So along with lower back muscles the abdominal and oblique muscles help protect the spine
stand on their head
Bladder is not situated below the kidney. It was situated posterior to the kidney. You have adapted the erect posture and so bladder came below the kidney. Actually it was posterior because it was convenient to have it near the outlet.
Yes, if you contract the right muscles.