You know what's funny, they may be called Arnold vacuums but I started doing them when I was in grade school back in the 70s. No one told me about them. I knew I was not FAT but I had a little bit of a gut so I figured if I concentrated on holding it in eventually it would get flatter; the muscles would learn to stay in instead of being extended out.
I remember one kid trying to give me sh*t on the playground during PE once. He

and said you are holding your stomach in. I said Yes and explained my theory. He stopped laughing.
I have not done these for quite a while but yes they work. Time to start up again.....