Intra-muscular tension is an interesting theory. While I think many more people (including my office mates) would have GERD if it were just from sitting in front of a computer all day, it could be a contributing factor.
Something I thought of in relation to intra-muscular tension is - what is the first thing they tell you to do with reflux? ELEVATE the head of the bed. What if this is actually contributing to keeping the LES open during the night? How many of you sleep with a wedge pillow (I put mine under the mattress to minimize the angle formed) with the intention of using gravity to keep the acid down? I know they tell you not to sleep on pillows - that it can make it worse - but what if there is no good way to elevate your head because your body needs to lie flat for the LES to relax and close?
What are your thoughts?