But it depends on whether you can persist.

I used to have a waist circumference of 80CM, and I have been doing it for more than a month. Now my waist circumference is 68CM.

They're all small.

Legs flat on the bed, PP sitting on the bed.

The whole person lies down, (equivalent to upside down)

Then get up like sit-ups. ..

Do as much as you can at a time and as long as you can.