(This piece is for my book-in-progress titled See How We Run: Best Writings from 25 Years of Running Commentary. I am posting an excerpt here each week, this one from August 2005.)
Last chapter advised letting marathon-day pace naturally follow the pacing of the longest training runs. For most runners those mile times are similar, and sometimes identical.
Here are more ways to predict your race times, these from one racing distance to another. Three physical facts underlie the three formulas below: (1) you slow by a predictable percentage as the racing distance increases; (2) your potential at the longer distances is set by your speed in shorter ones, and (3) you must train for the longer race, or none of these numbers will work.
– Half-Marathon Factor. I’ve long used this calculation, which says that your pace will likely slow by about five percent as the distance doubles. The easy way to do the math is to multiply the shorter time by 2.1 to predict the longer one. A recent two-hour half, say, would forecast a 4:12 full.
My first marathon team ran a half as its only race during the training cycle. Results from the 2.1 calculations were mixed.
Two runners hit their predicted marathon time exactly, and two others came very close. But the remaining dozen missed by as much as 24 minutes, with an equal number over and under. This isn’t an exact science.
– Ten-K Factor. My latest marathon team, now training for Portland, will have raced at least one 10K during this build-up. I’ll multiply those times by 4.8 as another way to see into the future. Under this formula a 50-minute 10K would make possible a four-hour marathon.
In the same month as my PR marathon, I raced a 35-minute 10K. It projected a 2:48 finish. I ran 2:49.
Much later my 10K time stood at 50 minutes. This said I’d run a four-hour marathon, and my time was 4:01.
– One-Mile Factor, more properly called the “Galloway Marathon Predictor.” More than a hundred thousand marathoners have passed through Jeff Galloway’s programs. He recently added a new wrinkle to this training: a one-mile run at good effort (after warming up well).
“We multiply these times by 1.3 to get a good idea what someone’s marathon pace will be,” he says. A seven-minute miler, for instance, could figure on averaging 9:06s in a marathon.
Running a seven-minute mile doesn’t mean you can sneak under four hours in a marathon without the right training. But the reverse is usually true. You can train well for that marathon but probably still not run a 3:59 if you’re unable to clock a 7:00 mile... or a 50-minute 10K... or a 1:54 half... or average 9:06 miles in the longest training.
Multiply out all of the formulas that apply to you. This establishes your realistic range of possibilities.
My purpose here isn’t to drain any of the mystery or surprise from your racing. You can know in advance what you might do, but never what you will do.
Mainly I want you to know going into the race what will be a reasonable starting pace for you. Running at that rate early will assure a better finish.
UPDATE FROM 2015
As a coach I estimate (based on longest-training-run pace) when our runners will finish. But I don’t tell them before the race about that predicted time; they set their own goals.
I only tell them the opening pace that will serve them best. Beyond the training, which is already in the bank on race day, and the weather that day, which no one can control, nothing has more to do with the final result than how well the opening miles are paced.
[Hundreds of previous articles, dating back to 1998, can be found at joehenderson.com/archive/. Many books of mine, old and recent, are now available in two different formats: in print and as ebooks from Amazon.com. Latest released was Going Far. Other titles: Home Runs, Joe’s Journal, Joe’s Team, Learning to Walk, Long Run Solution, Long Slow Distance, Marathon Training, Run Right Now, Run Right Now Training Log, See How We Run, and Starting Lines, plus Rich Englehart’s book about me, Slow Joe.]
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