"The stomach vacuum pose is a lost art in today's big time bodybuilding competitions. I haven't seen anyone do it on state in a very long time. It was my most impressive and memorable pose and I always ended my posing routine with it. But bodybuilders of today have such big muscular abs that they can only hang out. There's too much to suck in. But even they could learn to vacuum by practicing it. After all Mike Mentzer had a decent vacuum pose and he did Roman Chair sit-ups with a 50 pound plate. Certainly someone without too much waistline muscle could get a good vacuum if they practiced. Even more so if your waist is already small. here's how: There are 4 positions to do the vacuum in, each one more difficult than the one before. Easiest is lying with your head downward, such as on a traction table. I have one that declines down to 30 degrees and it is easiest to puss your stomach in because gravity gives you a boost. Years ago I hung upside down with gravity boots and found this to be the easiest position of all for vacuuming.
Next in difficulty is lying flat on your back. Completely exhale, forcing all the air out of your lungs, squeezing your abs at the end of the exhalation to get all the air out. Now instead of inhaling, suck your stomach in so far that you eventually feel like it is touching your spine! This is best done on an empty stomach. Practicing vacuums when you are hungry is an excellent means to get your stomach smaller and retard hunger as well. After you suck our stomach in, put your finger on the bottom of your ribcage and lift up and suck in some more. Hold it as long as you can safely. Don't go overboard and pass out. This is really a yoga "Panayama" technique for breath control. I was able to hold a stomach vacuum for almost a minute when I competed in the 1970s.
Next step is to do the stomach vacuum with hands on your thighs, bending over forward. Exhale completely and suck your stomach in, Hold it........... longer and longer ....... Good.
Now you are ready to practice vacuuming with your hands behind your head. If you are a competitor, this is a great way to attract attention. When the judges call for the abdominal pose (in which the hands are in the same position) hit the abs hard with hands behind neck, then vacuum quickly, then go back to the ab shot.
Doing vacuums may bring home the realization of how important the serratus muscles are for all poses with arms overhead. Dumbbell pullovers lying across a flat bench was what helped me develop my serratus and ribcage.
Stomach vacuums won't do much to develop your abs, that takes leg raises and crunches. What it will do is give you greater breath control and help you decrease the girth of your gut." - Frank Zane