Background: I wasn't the fittest kid -- still not as an adult -- and I wasn't fond of running, as I'd get exhausted quickly and/or get a side-ache/stitch. In general I avoided exerting myself.
On one occasion, when I was about 10 years old, I remember running home from school and not getting exhausted at all. This was about 1 mile. Normally, I could only get to maybe a 1/3 of a mile before I was out of breath and had to walk.
This really surprised me and I tried repeating it multiple times without success.
It felt as though my stride + heart + respiration were all in "sync", figuratively. But I couldn't figure out how to "resync" them.
Question: Is there a term for this? And/or training to improve it?