Stop sucking in your belly button.
Why this matters:
We were told as children to suck in our stomachs and stand up straight. However, years of doing this can result in having an extremely arched lower back, tight hamstrings, and pain. Sucking in the stomach would provide the illusion of a “smaller gut”, and standing up straight would result in us pulling the shoulder blades back and down.
In order for us to stand up taller, minimize pain, and strengthen our core is to do none of that.
Instead of sucking the belly button in (which often was believed to activate the transversus abdominus muscle), I recommend letting the rib cage downwards towards your pubic bone (the area just south of your bladder). Kind of like when you are laughing so hard that your abs hurt. When you truly laugh, your abdominal muscles contract, and your rib cage is pulled downwards. This lets your spine return to a neutral position while also creating some tension. A visual representation of this is found in bracing. This technique is something that I teach all of my clients to ensure that their spine is stable when moving.
Instead of holding 100% bracing tension throughout the day (which will cause other issues), try to maintain about 10-20% tension. This allows the spine to be supported when you’re standing or walking. The amount of tension is going to be related to the complexity of the activity or the weight you pick up. You also do not need to maintain this tension when sitting or lying down (there should be some passive support from the sitting/lying surface).