During the last half of my run, I experimented with arm-movement. I read the other day that arm movement is very important, because it influences movement of the legs. I've never had good arm movement, although I've noticed that sprinters really pump their arms.
I began to move my arms back and forth in sync with my legs. However, I noticed I was also twisting my body in sync with my arms. I concentrated on pumping my arms while keeping my body from twisting, and it felt like I was running faster. My GPS showed that I was, in fact, running about a minute faster. I need to experiment with this some more before I conclude that my increase in pace was due to my arm-movement.