12 mile EASY RUN

I tried to increase my mileage a bit. After a 6-mile run, I must say I was on cruise control and thought that I'd be able to finish my run for just under 2 hours. But that wasn’t to be, as both of my knees started to buckle down. I finished the run (and occasionally walking) disappointingly. And today, my knees are in agony. I think I need to give it a rest for a week and hope it’ll recover before the next EASY RUN. I need to consider putting down the mileage a bit in order to put less strain on my knees.