By Douglas Thompson Athletic performance breakthroughs are rare. For masters athletes, they may be even less common, since the athlete has already tried many approaches to improve their performance, and because time is constantly eroding what is possible. I seem to be experiencing one of these rare breakthroughs. It’s exciting, but I’m still not sure it’s going to last, and that makes me nervous. I am sharing my story in the hopes that some of you will share your own, and give me some perspective and insight into what may be happening. Since I began running track at age 44,…