When i flex my abs are clearly visable. But when i relax my lower belly protudes more than it did when i was 17-18 years old. Im 21 now. my body fat is low. What can i do to get that flat belly back even when im not flexing?

The secret to flat abs, when you aren’t flexing is to hold them in. In other words, since you say your abs are clearly visible when you flex, the reason the lower belly protrudes, is bad posture. Practice keeping your abs tight all the time, it’s really not hard and it will make your abs sharper when you do flex.

Train hard, Vince Andrich