The movements in this video can commonly be confused with doing a core work out or sit ups but it's not. Please please please drop any concepts you have of doing this to get a six pack or strengthening your core, and instead explore this video with curiosity. Instead of worrying about engaging your 'core', think about how you can change your organization and involve more of yourself into the movement so that it begins to become easier and more accessible for you. How can you find more mobility in your pelvis, ribs, spine, head and eyes so that your back muscles (extensors) can learn to lengthen and your front torso muscles (flexors) can learn to engage when required. Very heavily feldenkrais influenced and I know personally my back always feels a ton better after I do this kind of work.
If you come across questions or have some comments don't hesitate to share them with me!