This was the biggest test thus far for the VFFs. This was a pretty rough race, a lot of mud and rocks. Rocks up hill are no problem. The downhills are a little slower, because it is really hard for me to run on my forefoot going downhill. As you can see in the pic, I made a modification to the shoes. I had hoped the strings would keep my pinky toes in the toe pockets where they belong. It worked great till about the half way. There was a pretty long uphill. I had problems with both feet, with toes coming out. When I got to the top I fixed the left foot and it stayed, but the right one never cooperated after that.