I got home from my first real training run, and say what? My left forearm was burning as though I had just done 10 000 wall climbs (slight exaggeration). But seriously... Why does it burn? I was running the slowest I had ever ran in my life to try and stay in HRZ 2, so what was the deal here?

My guess is that maybe my fingers weren't as loose as they should have been. I was probably holding them wide open, and using those tendons in my forearms to do so.  Interesting...
This…