Rested Up

I'm rested up for the 50K on Saturday in California - maybe too rested. I went out to the park this evening to meet up with the group. It was raining, as it did all day, and no one else showed up. So, I went to Nautilus, worked out and then ran on a treadmill. That's the first time I have run on a treadmill in probably a couple years. How can anyone do distance on treadmills?