This is the "hollow" position we speak of. It's a another core stabilizing movement (like the GHD hip extension) that allows us to train the core generally and the abs specifically for their real role in human movment: stabilization.
A couple of ideas for increasing the difficulty of the hollow body position, from Gymnasticswod
Today is the one year anniversary of the helicopter crash that killed 31 service members. "The 31Heroes Project came about in response to the Chinook helicopter crash that took place on August 6, 2011 killing 30 military service members and one military working dog." For more information about the 31 Heros tribute WOD, go here: http://www.31heroes.com