The abs bring the pelvis and rib cage closer together. Strong abs do this. Weak abs don’t. Unfortunately, there are a lot of famous workouters with super weak abs who have been teaching millions of people the exact wrong thing for decades. It doesn’t matter how “good” the person looks. It doesn’t matter how lean they are, how famous, how athletic they seem. If they cannot control flexion, they are weak af through the abdomen. For a closer look, watch the video and observe the photos here: https://www.instagram.com/p/CWGkaDUFsbh/?utm_medium=copy_link
A visible six pack doesn’t mean the person is strong. It means they’re lean. Watch closely; and you soon see they never hit flexion. They can’t. They’re weak. Moreover, they do a lot of what we professional strength coaches call “wet noodle”. Because of the weakness and instability throughout the midsection, they wriggle and waggle a lot. Hips rock and twist. They’re a wet noodle. Their followers tweak their backs and wonder why. Because the popular example is incorrect.
Start by watching yourself from the side in a mirror; and practice flexing the trunk. Start by doing kneeling “cat backs” on the ground. Always and forever remember flexion.