Shrink your waist by performing one simple exercise: the vacuum. To train the transverse abdominis (TVA) start with the easiest, most basic version of the vacuum. Perform it supine (face up) to get the assistance of gravity. Here's how:
Lay on your back with your hips and knees flexed such that your feet are flat on the floor or bed.
Exhale as much air as possible. This raises your diaphragm and, much like an empty stomach, allows for maximum contraction of the TVA.
Pull your navel in as close to your spine as possible. The more you can draw your navel in, the more the TVA contracts.
Try to hold the vacuum for about 15 seconds or so on each set. As with any exercise, you'll want to progress over time. Work up to holding the vacuum for 60 seconds each set.
Don't let your inability to hold your breath keep you from doing these longer sets. Take small breaths as needed.
Graduate to doing the vacuum on your hands and knees, then seated, then standing.