Sit-ups are in the past. I'll introduce you to a new action called double start.
From both ends, are you lying on the mat or on the bed! Legs up. Lift your upper body, too! The body is u-shaped, reaching the toes with your hands)
10 Start from both ends and make 3 groups! This action is laborious, because you are not used to it, so don't be strong.
Slowly, it can increase at a rate of five. This action can fully stimulate the abdominal muscles! Do a few will feel sour!
If you keep practicing, I promise you will see the effect in a month. This action is generally a professional training subject.
It's all from experience. If you don't believe me, try it. The result is the best proof. You can send me a message if you don't understand, and I will try my best to help you.