Through the years I have heard to press the lower back to the mat and then I hear that it is better to keep the back neutral. I had heard that keeping the back neutral creates more of a challenge and we work more of the ab muscles.
Agreed, neutral spine is the preferred position when working the core, while attempting to access those ‘deep’ core muscles that one can not get to via typical ‘crunches’. This allows protection of lumbar spine health, which for many people is where the back pain issues begin!