The Stomach vacuum by Judith Samama-Patte :

“I'm going to take a lot of precautions here, because these exercises have to be done properly to avoid hurting yourself, and have to be performed with care and caution. The “stomach vaccum” (otherwise known as hypopressive abdominals) massages the internal organs to detoxify them. The result: better digestion, less bloating and deep abdominal strengthening. You can perform between five and ten cycles of these abdominal exercises in the morning on an empty stomach. Do not do them after eating." 

1.

INHALE through the nose by inflating the belly.  

2.

EXHALE air from your lungs by pulling in your stomach, stopping just before you run out of air. 

3.

HOLD YOUR BREATH for ten seconds or so with your belly tucked in, as if you were trying to stick your belly button to your spine.

4.

RELEASE and rest for a few seconds, breathing normally before starting a new cycle.