I ran a 1:30 half marathon two weeks ago (6:55 pace or so), so I should have no problem running just one 7:10 mile, right?
Here's what happened. I ran 8 miles Saturday. Came home, cooled down, ate lunch and an hour later I threw a football with my son. We decided we would run a timed mile together on a track. He runs a low 7 minute mile. I did no warm up.
Running a 7:10 pace, I could barely keep up with him for one lap. I was hurting as if I were all out sprinting - my lungs and heart felt like they would explode. I was in serious pain. I had to step off the track while he ran the second lap by himself. I ran the third and fourth lap with him, but I was in major pain. I could barely keep up the last lap and ended shorting the course. He ran a 7:10. I don't have asthma.
The problem was either a belly full of lunch or no warm up, right? Wow, I had no idea (even after years of running) how much those factors could affect performance.