Here our model has over tucked her pelvis. This is a common habit in exercise, but ultimately it is very limiting. It is a position that does not stabilize the pelvis or work the abdominal muscles in optimal ways.
You can see that if a plate were set on our model's lower abdomen, it would not lie flat, it would tilt toward her belly button. In order to get her pelvis this tucked, our model has engaged her hip flexor muscles in a way that is going to inhibit freedom of movement. There is too much tilt to the whole pelvic structure.
This position might look familiar. Lots of people end up here when they try to do exercises like crunches, or the Pilates roll up and chest lift. This position makes it harder to get up, and harder to work the muscles you really want to work, like the abs.
On the next page, we look at an even more obvious version of the same problem....
