First of all, there is no fastest way to practice abdominal muscles. If you want to practice, you must persevere, because the abdomen is the easiest place to store fat, and the abdominal muscles recover the fastest. If the strength is not enough, it is just tickling for the abdominal muscles. Only by persistent practice and ensuring strength can you show your muscles.

Secondly, you said that you think sit-ups are ineffective, which is impossible. Then you are not strong enough, then your actions are wrong. Sit-ups are not as simple as watching. When you do movements, you completely use your abdomen to drive your upper body. When doing it, the legs drive the abdomen to lift the upper body, and the hands and head don't need any force. Only in this way can you achieve the stimulating effect. In the process of abdominal muscle contraction, try to feel this contraction with consciousness. When many people do it, they actually bring it up with the strength of their waist and neck. This is a big misunderstanding, and there are many other ways. Sure, you can check it online. Generally, abdominal muscles can only be exposed when body fat 12%, so this is a laborious process.