That is a very fast pace. On one of my runs I started cramping very badly. I could not understand why it was happening. I was hydrated and did not do anything out of the norm. I ended up going to the doctor then blood test revealed I had chronic kidney disease. This was certainly an adjustment in what I ate an how I trained.

As I get older I become to the realization that I can run like I use to. Am now I am okay with that.