My Saturday run was a great run for "arm swinging". I practiced the "arm swinging" for almost the whole run, and I had a natural synchronization between my arms and my feet.
Today, except for a mile during the warm-up phase of the run, I had the natural sync today, too. During that mile, my arms kept getting out of sync with my legs, and I felt like I was floundering. I had to focus on my right arm and forget my feet and other arm. It wasn't long before I was back in sync with my arms and legs. I noticed today that I was starting to automatically go into the "arm swing" without having to tell myself to do it.