Since running the Steamboat Marathonon June 1st 2008, I had not run long. I'm a little surprised I've been running as much as I have been, when I remember back to the feeling of burnout leading up to and following that difficult course. So Friday, to celebrate Independence Day I decided to stay in touch with longer runs by going out for a nice easy 10 miles.
When I left the house at nearly 11:00 a.m. it was already 80 degrees and when I finished it was 85 or 86 degrees. It was a Colorado blue bird day and the sun was intense. My plan was to stay real slow and easy. To make sure of a slow pace, I wore more Garmin 305 and heart monitor and walked for one minute for every 4 minutes of running. This kept me at a pace of about 9:15 per mile with the last couple of miles at about a 9:45 per mile pace. For me, that is 1 1/2 to 2 minutes slower than marathon race pace and is typically a relaxed run. I keep my pace in that range generally for long training runs between 10 and 29 miles. I tell you that so you know that I have a lot of experience at that pace. I know what that pace feels like and I have a very good idea of where my heart rate is generally on a run like that.
For instance, I ran the Journeys Marathonon May 10th and thru the first half of the marathon my pace was around 9:30 per mile. My heart rate never exceeded 155 and was in the low 140s much of the time. The temperature that day was between the upper 50s and about 70 degrees at the finish. My average heart rate for this marathon was 135 bpm.
My average heart rate on my 10 mile run last Friday was 146 bpm and after 3 miles I was hitting 161 or higher during some part of every mile. My final mile I hit 171 bpm. That is a significant increase in heart rate and the only significant difference between these runs was the temperature.
To put this into proper perspective, I can run 1 mile repeats at a 7:20 pace while keeping my heart rate right around 162 or a bit lower. When my heart rate moves much higher than that, I am unable to maintain performance over a long haul. So as my heart rate hit about 160+ bpm after about 4 minutes of running, I was nearing my maximum sustainable pace, which turned out to be about 9:15 per mile when the temperature is 85 degrees. That is 1:32 per mile slower than I averaged in the Country Music Marathon when the temperatures were in the 50's and 60's. WOW! What a huge impact from heat.
No wonder I love running in cooler weather. But, here is the real take away. Expect a lot less in hot weather because your body is working harder, even when your pace is slower. So keep it slow. You are still getting the benefit of a faster workout because of your heart rate.
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