If the hills are very short, I don't always adjust my posture, and with enough of that, that can mean really over-using the hip flexors. I particularly notice it if I'm running on a one-mile paved trail that I sometimes use - the rises are very short, 10 feet or less, which is why I'm nearly to the top before I start increasing my lean - but they're steep enough to notice, especially after a few laps. Something to think about ...

I'm also in the midst of a years-long process of getting my feet to actually function as feet again. Yoga, stretching, strengthening, barefoot and minimal-shoe walking, mobilization exercises, intense massages and self-myofascial release, thinking about my posture pretty much ALL the time... Based on my experience, and the reading and TE discussions that brought me here, I would definitely encourage everyone to try to do that, barring real structural problems. The sooner you can get yourself out of the rigid shoes, the sooner your whole body can work the way it's supposed to. Rigid and mis-aligned feet and ankles have consequences all the way up the kinetic chain.