I found an awesome exercise for building up my lower abdomen
Muscle isolation.
Basically, relax everything, and contract only what you want to build up. Having a comfortable posture helps though.
Lay on your back, with your spine long and as flat to the ground as possible. relax completely into this position. then, lift your legs by contracting only your lower abdomen.
when you contract a muscle, breathe in. when you relax and return to the start position, breathe out. Legs can be bent or straight, the important thing is feeling comfortable.

Slower the better.
anyway. that's what I'm currently doing. may not work for all posture types, but it's working for mine at the moment

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