Just talked to my boss, a respected neuroligist, about selective activation of the muscles of the rectus abdominus. It is quite possible to contract just the upper, or just the lower portion, and, with significant training, one could probably learn to just contract each group of muscles in between each "square" of tendinous inscriptions. He described the way they are wired to the brain and how it allows for it.
Thank you for your time.
Thank you for your time.