I too have been running this race for a long, long time, and I have to say that I didn't have any problems with uphill runners yielding when I came down. I did have some problems with downhill runners, when I was coming down as well, who weren't going downhill as fast as I was and refused to yield to let me by, even after repeated requests from me. To answer your question specifically, there is definitely an art to the ability to keep moving and yield to downhill runners at the same time. What I noticed most this year is that the uphill runners are getting out of the way, but they've lost the art of continuous upward progress while yielding. I believe yield means get out of the downhill runner's way, but if there is room for both the uphill and downhill runners to pass by each other, than by all means keep moving! Squeeze yourself as far to the right of the trail as you can, but keep moving. If I was frustrated by anything this year it was the amount of uphill runners who were coming to complete stops to let downhill runners by, when there was clearly room for both to pass by cleanly. This was clogging up traffic behind the stopped runner. If it is an obvious tight spot where only one runner can get through, then yes, you should come to a complete stop and let the downhill runner pass by unimpeded. Lastly, it's extremely helpful when all of us uphill runners yell out "runner" or "runners" to alert those around us that a downhill runner is approaching. I don't like getting stuck behind people that stay silent on the uphill, and then just when you step to the left to get around them you about get killed by a downhill runner. Very frustrated by runners who are in the position of having the vision on the trail not alerting runners around them. All in all, I think most everybody is pretty considerate and tries to get out of the way. I think most collisions or near collisions are unintentional usually caused by uphill runners who are either just "out of it" because of the altitude, or as I just mentioned above, an uphill runner coming out of a blind spot and moving to the left of the trail to pass a slower runner, and not realizing that a downhill runner is bearing down on them at almost that very moment!
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Each year I wonder, does "yield" mean actually stop or just move as far out of the direct path line as possible but continue forward if room is available?