muscle building... could that be part of this too?

You should try Pilates breathing and "powerhouse activation" exercises in this goal

Since my wife teached these basic principles to me, used in conjuction with my anerosing, it has been like a second revelation about my body (especially for the part you're talking about).

---> Wiki quote : http://en.wikipedia.org/wiki/Pilates
"...
[h=3]Breathing[/h]
Breathing is important in the Pilates method. In Return to Life, Pilates devotes a section of his introduction specifically to breathing "bodily house-cleaning with blood circulation".^[19]
He saw considerable value in increasing the intake of oxygen and the
circulation of this oxygenated blood to every part of the body. This he
saw as cleansing and invigorating. Proper full inhalation and complete
exhalation were key to this. "Pilates saw forced exhalation as the key
to full inhalation."^[20] He advised people to squeeze out the lungs as they would wring a wet towel dry.^[21] In Pilates exercises, the practitioner breathes out with the effort and in on the return.^[22] In order to keep the lower abdominals close to the spine; the breathing needs to be directed laterally, into the lower rib cage.
Pilates breathing is described as a posterior lateral breathing,
meaning that the practitioner is instructed to breathe deep into the
back and sides of his or her rib cage. When practitioners exhale, they
are instructed to note the engagement of their deep abdominal and pelvic
floor muscles and maintain this engagement as they inhale. Pilates
attempts to properly coordinate this breathing practice with movement,
including breathing instructions with every exercise. “Above all, learn
to breathe correctly.”^[23]

[h=2]Powerhouse[/h]
Students are taught to use their “powerhouse” throughout life’s daily
activities. According to Joseph Pilates, the powerhouse is the centre
of the body and if strengthened, it offers a solid foundation for any
movement. This power engine is a muscular network which provides control
over the body and comprises all the front, lateral and back muscles
found between the upper inner thighs and arm pits.

The Powerhouse is activated effectively by hollowing of the deep
abdominals, by drawing the navel back into the spine in a zipping-up
motion, from the pubic bone to the breast bone thereby engaging the
heels, the back of the inner thighs, the deep, lower-back muscles, and
the muscles surrounding the sitting bones and tailbone area without
inhibiting the natural function of the diaphragm—that is without the
practitioner holding their breath either from lifting the chest upwards
or contracting the chest.
..."