Delaying a meal brings about symptoms most people call "hunger." These symptoms include abdominal cramping, weakness, and feeling ill-the same as during drug withdrawal. This is not hunger. Our dietary habits, especially eating animal-protein-rich foods three times a day, are so stressful to the detoxification system in our liver and kidneys that we start to get withdrawal, or detoxification, symptoms the minute we aren't busy processing such food. Real hunger is not that uncomfortable.
The activity of both sets of muscles, the diaphragm and the abdominal muscles, varies reciprocally. Thus, during inspiration the tonus of the diaphragm increases while that of the abdominal muscles decreases, and vice-versa during expiration. Hence there exists between these two muscle groups a floating equilibrium constantly shifting in both directions.
Consider the oddity of those drug commercials on television. Fifteen seconds of the purported therapeutic effort, followed by about 45 seconds of a rapidly muttered list of horrific possible side effects. When the ad is over, I can't remember a thing about what the pill is supposed to do, except perhaps cause nausea, liver damage, projectile vomiting, a nasty rash, a four-hour erection, and sudden death. Sudden death is my favorite because there is something comical about it being a side effect. What exactly is the main effect in that case? Relief from abdominal bloating?
Core strength and stability is very important to me. Tennis is all about rotation of the body and my ability to create power. I incorporate a lot of abdominal, back and glute exercises into my gym sessions.
I think that we pay much more attention to fashion and our hair, skin and foreheads, our abdominal muscles and shoes than what is happening in the world. We willingly take that 'drug' and go along with that.
Some animals on Earth regurgitate as opposed to vomit, i.e., stomach contents flow up into the esophagus without any forceful abdominal contractions. What I experienced in zero gravity was similar to this, expulsion without the heaves.