Mileage Accuracy

Tuesday, October 22, 2013 | By Hal Higdon
 
 
 
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Got a question about running? You're in the right place. Every Tuesday, world-renowned coach, author and athlete Hal Higdon posts and answers athlete questions here. You can submit your question by joining the discussions on Hal Higdon's Virtual Training Bulletin Boards.

QUESTION:

What is a good plus/minus for the long runs? Obviously, even with a good GPS watch (which not everyone can afford), there are variations especially in the valleys of Vermont where I run. I was able to measure part of my 20-miler yesterday on my watch, and the GPS for my iPhone measured the run at 20.2 miles, but the part of the course that I could drive indicated the workout was only 19.8 miles. I know that this is not a large variance, but what is acceptable? And, although it is late in my program to be asking, how do other runners measure their mileage?

HAL’S ANSWER:

Badly, some of them, I suspect. But I'm not sure it makes much difference as long as you or they are consistent in your and their inaccuracy. Scientists I know would label your numbers as “statistically insignificant.” (Yes, I know, scientists sometimes are rude in their use of language.) If you lived in Chicago along the lakefront or the Prairie Path, there are accurately measured mile markers. Otherwise, GPS watches do a reasonable job of being close, unless you are surrounded by skyscrapers or in the woods when they can be wildly incorrect during portions of the run while blocked from those magic satellites overhead. And didn’t I just see a Sandra Bullock and George Cooney movie, where a bunch of satellites got knocked out of the sky? So don’t worry. As long as you are reasonably close to the mileages in my training programs, I suggest, you'll do fine.

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