The 19:45 PR was set after an injury that had me out for three months. All I did during the three months was cycle 10 miles a week (I was almost basically next to sedentary). I came back into running by running 3x a week at 8:30 pace, the next week 3x at 8:15 and for the next week weeks 3x 8:00-7-40 pace. The week after I decided to do a mile time trail to see where I was at and I completely blew myself away with a 5:25 PR (my previous attempts were in the 5:50-6:10 range and had only tasted sub 6 a couple of times prior. Two weeks later I raced a 5k and went sub 20 for the first time.
I had a massive surge of fitness that came out of nowhere which I 100% contribute to taking a break and allowing my body to recover for a few months. I felt very burned out and overtrained before the injury (feeling sleepy during runs, thyroid abnormalities, no energy, trouble sleeping).
Naturally, after experiencing this totally unexpected gain in fitness I wanted to maintain it so I ried to do so by uppimg my milage from 10-15MPW (3x3-4 mile runs at tempo or sub tempo pace with a long run) to doing 4 easy runs a week with strides occasionally, a tempo every ten days and a long run for milage for 4 months. I bumped up to 40-45 MPW during this.
Then after that I eased into a plan where I am doing 25-30 MPW consisting of 3 easy runs a week at 9ish pace with strides (200m@40s), a long run, a tempo and one or two track sessions 400 repeats at 5:25pace or 800 repeats at 6:15pace so essentially, I think I was training quite well but then the fitness seemed to deminish and I could no longer keep up with my workout paces.
Somebody asked my sprint ability. Recent times on a track have been:
14s 100m
33s 200m
73s 400m