<human>: Summarize the given text in a few sentences.

A couple weeks ago, after a fantastic 19 mile run, I noticed my right knee was starting to hurt quite a bit. I suspected it was due to a new loop I had recently added on to my regular route to shake things up a bit. My regular route is almost entirely on sidewalk, but this new loop took me on a road with a nice wide run/bike lane for about 3/4 mile. I'd been running on that new loop quite a bit, and had done it 5 times on this 19 mile run.

I really liked the new loop, but I noticed that it made my right leg tired due to the camber of the road to the outside. Even though the road itself is well-maintained and reasonably flat, just the slight incline to the left (since I run on the left side of the road) was enough to force me to slightly pronate with my right foot. This is something I notice any time I run on a road for a race, but it usually isn't that big a deal, since it's just for one day. In this case, I'd been running this new loop quite a bit for a few weeks, and the 19 mile run really sharpened the effect it had.

So, I iced up my knee, took an extra rest day, and stopped running that loop for a while (I might bring it back at some point, but not run it as often). My knee is much better now, although there's still a little pain.

I know I've read here and elsewhere that a road surface is (slightly) better to run on than a sidewalk surface, in terms of how hard it is on your joints. That may be true, but I wanted to offer my experience on it. I think the way the surface slopes is something that needs to be taken into account.

So this may seem like kind of a boring story (I fell asleep reading back through it), but just in case someone is having problems with one leg and not the other, it's something to consider as a remedy :)
<bot>: I've found that whether a running surface consistently slopes to one side or is flat is more important than the material of the running surface, in terms of keeping your joints feeling good.