[xenocratus]

> Lately every few days I go outside and run hard to beat my last time (currently PR is 28:10). [...] a few days ago [...] I suddenly had a terrible calf cramp that took a few days to get past.

As someone with horrible back pain issues after a very intense block of training for a 1/2 marathon at the beginning of this year, I do hope you'll reconsider that first part of the quote above, since it's probably one of the causes of the latter. Took me a while to internalize the "run slow to run fast", but it does make a huge difference for injury prevention.