The first exercises you would do in a pilates workout is The Hundred. It strengthens your abs and increases your circulation and prepares you for the other mat exercises. It is an excellent exercise for reducing that belly. Done correctly, you should feel the strain in your abdominal muscles, not your back. If your back hurts, then you’re not doing it right.
Lie on your back, straighten your arms and bend your knees at right angles with your calves parallel to the floor and your arms by your sides.
Straighten your legs and point the ceiling with your feet. Your heels should be together while your toes stay apart so that your feet form a v-shape
Lift your head off the ground.
Lift and lower your arms in a pumping motion, 5 times while you inhale, 5 times while you exhale for one set.
Do ten sets continuously, so you will pump your arms a total of 100 times, hence the name The Hundred
A few points to take note of.
Pull in your stomach throughout the exercise. Imagine your are pulling your navel to your spine.
When you exhale, try to squeeze out all the air from your lungs
Relax your neck and throat when you do this exercise.
The first time you try this exercise, if your abdominal muscles aren’t strong enough, you might not be able to do the classic way. To make it easier, you can rest your feet against the wall until you get the hang of it.
Doctor Charles Drew Medical Blog 