When I worked at the old gym, any exercises with bringing both legs down at the same time while lying face up were out. That’s because not many people can do it properly. This does only harm you but training. I will explain how you should perform it but if you are not sure, I will teach you during personal training sessions.
Learn the hip position
Lying down on the floor with face up, the knees bent and the feet placed flat. Then place your hand right under the lower back to learn the neutral position of the lumbar spine.
To teach yourself what anterior pelvic tilt, go back to lying down position, try to create excessive curve on the lumbar and the spine (anterior pelvic tilt) .
What you want during most of the core training is the opposite (posterior pelvic tilt ) So now you try to contract the abdominals as tilting hip posteriorly, You will know once you place your hand under the lumbar spine where there should be no space.
Progressing by doing Deadbug exercise
Deadbug is a great way to learn how the core stabilizes. Lying down with face up, engage the core muscle with posterior pelvic tilt position, bringing the both leg up in the air and the knees are bent 90 degrees.
Exhale while slowly lowering one leg toward the floor and maintaining a bent knee position. Making sure to avoid any loss of lumbar stability throughout the movement. Hold the position briefly before returning to the starting position. Repeat this save movement with the opposite leg.
Progression of Deadbug
The starting position, but raising an arm as the diagonal side of the leg is bringing down. Don’t forget that the main objective here is to learn how to stabilize the core. If you start losing it, take a break or go back to the previous version. And don’t do it while feeling pain.