Lie on your back, lift your legs, lie flat, put your hands on your sides, straighten your legs, and use your abdominal strength to drive your legs up until they form a 90-degree angle with your body.

Step on a bike

The legs are bent at 90 degrees, and the thighs are at 90 degrees to the abdomen. Keep your head and back as far away from the ground as possible. Keep your legs off the ground and do something similar to pedaling a bicycle.

I don't know the name of the other action, so I'll teach you:

The upper body is close to the ground, and the legs are lifted and straightened at 90 degrees with the body, that is, the feet are straight to the ceiling! !

Then lift your hips off the ground as much as possible with the strength of your abdomen and back. It's best to take them back to the north and cancel them.

Excerpt from my answer to others!

Practice hard!