WHY DON'T MILE MARKERS MATCH UP WITH MY GPS?

DAVE MCGILLIVRAY, for Runner's World

I am a 21-year-old female runner, and I have completed two half-marathons and two full marathons. I am a PR-seeker and eventually would like to qualify for the Boston Marathon. One of my biggest problems with achieving a PR during a race has to do with discrepancies between my GPS watch and the race-course measurements. I do all my speed training with a GPS watch, and by race day, Iam very familiar with running at my intended race pace. However, when I get onto the course, I find the mile markers almost never match up with my GPS. As a result, I either end up going out too hard in an attempt to keep up with the course clocks, or go the pace that I practiced in training and don't end up achieving my goal time. Could you shed some light on how to solve this problem? - Kristin

Kristin. I've received several e-mails from runners in races I have directed stating that the course was too long or the mile markers were off. Even though the courses were certified by an official,  experienced USATF certifier, these runners are adamant that they are right and we are wrong.  When an experienced USATF certifier measures my course, I believe 100% that the distance and mile markers are accurately measured and the distance is what we have advertised it to be. 

When there is an apparent discrepancy, as in your case, several factors may be to blame:

Some courses have a lot of turns. I have found that most of the time when someone who wore a GPS device claims that the course was long, the course they are referring to probably did have many turns. It is almost impossible for someone to run the course exactly the same way the course was measured, especially if there are a lot of runners in the race.  Unless you are running alone and there are no other runners near you in the race, most of the time you can't always run the tangents the way the course was measured. Thus, you are actually running a longer distance. But that doesn't mean "the actual measured course" is long. Additionally, sometimes runners begin their measuring from the spot where they are lined up at the start, which is not always exactly on the starting line itself.

Interestingly, some GPS-wearing runners have also claimed that a certified course could actually be a little short. Perhaps their readings were off as a result of losing contact with a satellite because of trees or tall buildings blocking the signal for a short period of time. 

So, whereas the phenomenon of GPS technology has added some unique, valuable, and fun aspects to running, don't be fooled into thinking the course is not accurate just because your GPS indicated something different — these devices are not always right, either.

UPDATE: One thing I failed to mention earlier... If the course was not certified, then the distance may, in fact, be off.  And even if the course was certified and the mile markers marked properly on the road, a race may mistakenly sometimes place its mile marker indicators in the wrong locations.