I'm interested in tracking as much data about my runs as I can in an effort to get faster, and while I can easily estimate energy expenditure during an uphill run due to the change in elevation, I can't estimate energy expenditure due to the requirements of just keeping in motion. I could estimate wind resistance, creating a simple cylindrical model and estimating drag, but obviously it would take energy to move forward on a flat surface in a vacuum as well.
Where would I start for this? What would be my variables? I know for a bicycle it's pretty simple to account for rolling friction, but I'm not sure what I'd need to account for. The question: What makes running so much less energy-efficient than bicycling? seems to downplay the importance of vertical motion in energy dissipation.
I guess to further boil down the question I'd ask: where does the energy go when you run?