Endurance run

Today's treadmill run was not as good as yesterday's. I was at a 7:00 minute mile and could not get my heart rate over 168. I was supposed to have fartlek intervals but the run ended up being simply a 35 minute endurance run. I think that I will start replacing one of my longer bikes with a long run to try to train up for the Philadelphia 1/2 marathon. I feel like I have unfinished business from Cancun, it's kind of funny since there was an article that addresses this in this months Runners world. There is probably an article in the vein every month....but this time is feels pertinant.