I like to visualise the core as being similar to a wooden whisky barrel. As the image above shows, the barrel (Core muscles) acts as a protective housing for the spine. The top of the barrel is your diaphragm and the bottom is your pelvic floor. The wooden struts making up the sides are your trunk muscles, rectus abdominus (abs) and back extensors (including the multifidi). The metal supporting belts are your transversus abdominus muscle and obliques muscles.
Now imagine that the metal belts were removed (weak transversus abdominus and obliques) and the top and bottom were weakened (poor use of diaphragm and pelvic floor). What do you think would happen to that barrel if it were jumped on top of? …. it would collapse. The same goes for your torso – it would slouch and/or lead to uneven overload on the spine.
How to engage your core correctly and how using your breathing can help.