How to do Stomach Vacuums:
• Stand straight with feet shoulder width apart and hands on hips.
• Inhale deeply.
• Exhale while contracting your stomach muscles so that it looks like your navel is trying to touch your spine. Hold this position for 5 seconds while exhaling. That is 1 rep.
I find this exercise is great for making my stomach flatter, and it only takes a few seconds. Some people recommend exhaling completely before holding the position for a few seconds, I advise against it as a lack of oxygen to the brain isn't exactly very healthy. This exercise is great because you can do it anywhere, just make sure you practice in front of a mirror first so you don't look like you're constipated.
Equipment I use for this exercise: None