One thing I notice if I don't keep my abs pulled in is that more weight goes into my hands and I don't sit as strong on the bike. I roll along but am not as in control of the bike - more reactive. I just try to remember how I feel and what it feels like to pull everything in. I'm not talking crunching while riding - just making sure the core muscles are engaged. my torso lengthens and my breathing is easier and my back feels much better with the support!

I don't know if that helps at all. I'm still working on paying attention to my riding possition. I don't road ride - it's all mountain biking so I move around a lot. It's a constant effort to remember!