Sit-ups can exercise abdominal muscles well. ..

Lying on the ground and standing up can better exercise the lower back muscles. ..

As for the back muscles, ..

I forgot the name of the action. ..

But I can teach you how to move. ..

Feet apart. ..

Focus on the front foot ..

The upper body leans forward slightly ..

If your left foot is in front, hold the dumbbell in your right hand. ..

Move up and down, try to stick your arm to your waist. ..

That's about it. ..

It doesn't need to be fast, as long as it is in place. ..