9 Miles at 8 minute pace

Ran on Sat with a buddy of mine and we did 9 miles in 1:12. I was feeling pretty sluggish and not entirely sure why. The pace is ok, but I felt like I was pushing it. HR was at 145, so it was more my legs were tired. I believe this has more to do with bumping up the training load. I would like to get my training times down to 7:30s in the near future for the longer runs.