In my post on Monday about Ice Mountain, WV, I alluded to walking during uphills as a time of rest. I don't think I did that topic justice so I wanted to amplify that a bit here.
The top dogs in a Ultra trail race do indeed run the whole thing, or nearly so. But for those of us in the middle to the back of the pack, walking makes up a significant part of the forward motion.
My strategy is to try to run all the flats and the downhills, walking the uphills and any places where the footing is bad (e.g., rocks, roots, stream crossings). For me, that typically translates into running about 75% of the time. Thus in a 100 miler I'd cover 75 miles while running and 25 at a walk.
What makes the uphills so gratifying and why I look forward to them is the idea of a respite from running. Although it's still an uphill trudge and a significant effort, the contrast with running is marked enough that it seems like I'm taking a break. A long uphill--say a mile--will take some 15 minutes to walk, plenty of time to be ready again to break into a run upon reaching the top.
This just proves that everything is relative.