can not flexing your abs make your back round when deadlifting?

[audiophyle]

i read this somewhere on the net, not sure where. I've had a slight pain developing in my lower back when deadlifting even though i try as hard as i can to keep my lower back arched. I'm wondering if it's from not flexing my abs enough during the movement. what do you think?

 

[overhead]

I know when I lose my air my back seems to always start to arch soon afterwards

 

[Liftbig]

yes