Saturday I ran the Super Run 5K and set a PR. I was amazed that I could run 3.1 miles in 22:36, 7.17 pace. I almost never run that fast. I started second guessing the course measurement. But decided it must have been close since Jesse and Jim's times were on par with their prior perforances. So I had convinced myself that I had really lowered my time significantly.
Then, I did my speed workout today. I went over the old dirt track at the local junior high. There are no lane markings and I'm making the assumption that it is a standard size track of 400 meters (440 yards) therefore 4 laps per mile. I did 5 - 400 meter speed laps with a recovery lap in between, just like a couple of weeks ago. I did the laps in almost the same times as before, but I was beat at the end of each lap. I walked the curve during the recovery, then jogged on. Then I started calculating in my head, 4 laps at just less than 2 minutes a lap ... that's less than an 8:00 mile but well over a 7:00. Right?
When I got home I added up the time for the 5 speed laps (9:06), divided by 1.25 miles and come up with a 7:17 pace. The same pace I kept in the 5K. The thing that bothers me is that during the 5K, I felt good, a little pushed beyond normal but not exhausted. At the track I felt pooped after only a 1/4 mile and looked forward to the slow lap.
Am I doing the math right? Why does a 7:17 pace on the track seem much harder than the same pace during a 5K race? I'm probably oversimplifying or misunderstanding some basic concept. What gives?