Technique of the exercise:
You are lying on your back with your legs hooked (knees bent), your feet hip-width apart. Hands resting behind ears with elbows apart. Before starting any rolling movement of the back, you should remember to pull in your stomach (suck in the navel), then take a breath and breathe out (through the mouth with pursed lip) as you start the movement.
Do not force the flexion, it should be approximately 30 °. The more you go up, the more you will work your hip flexors.
At no time should your lower back lift completely off the ground.
Main: rectus femoris (Abs)
The exercise is felt more generally in the upper part of the rectus abdominis (sternal part), but theoretically the curling of the back allows you to work the lower part as well (but the feeling of work is less felt).
The transverse will also come into play if you focus on trying to tuck your stomach in throughout the exercise.
Interest of floor crunch
The most famous exercise for working out those abs is the crunch. Its ease of execution and the lack of material requirements have a lot to do with it.
Variants of floor crunch
The exercise can be done with the hips flexed 90 degrees:
Or on a declined bench:
Finally, it can also be done by weighting to increase the difficulty even more (the weights usually put behind the head).
Finally, the exercise can also be made easier by changing the placement of the hands (in order of ease: arms extended in front of you, hands crossed on the chest, hands behind the head, arms extended behind the head).
Danger / contraindication
If the execution instructions are followed, there is no real risk. But it is always good to make sure that your belly is tucked in throughout the exercise and not to raise your chest too high, otherwise the hip flexors will work (risk of back pain). .