I’ve got a little rant. And to be fair, I used to think the same way as the people who do this when I first started running. But enough already.
Garmins and other GPS watches/apps are fantastic tools to help with running. They are pretty amazing devices. But they are not infallible. The way the technology works is pretty darn smart, but it is hardly precise enough to rely 100% on. Basically, the watches ping off satellites far, far away about every 10 seconds and are able to to mostly pinpoint where you are located. But there can be a lot of “noise” around those signals, including trees, buildings, even by so many other runners accessing the same satellite simultaneously, etc.
Most race courses are very, very carefully measured multiple times by nifty gadgets used on a bike. These measurements are often certified. And also, these measurements are going to be a heckuva lot more accurate than your Garmin. [An aside, your Smartphone apps are usually even less accurate than a dedicated device like the Garmin. I used to run using both, and the phone app was always more optimistic about my pace. I recently ran with a friend who uses Runtastic, and his data said we ran 5.7 miles while my Garmin said we ran 5. Boy was he bummed.]
Have you ever looked at the mapping of your Garmin data after a run and seen that it looks like you cut corners when you know you didn’t? Or as if you ran through a building? Go ahead and look at your Garmin data for a race you felt the course was long or that you ran the tangents poorly. See if your running map closely matches the actual course.
I just ran the Rock n Roll Philly half marathon on Saturday. The first three miles were in the middle of Center City.
My Garmin beeped about a minute before I hit the first mile marker. No, the mile marker was not wrong. My Garmin was wrong. Here’s a graph of those first few miles. See how erratic it was? I promise I wasn’t jerking along the race course, going uber fast then stopping.
I have no idea what was going on here. I was stumbling through Philadelphia, apparently. I won’t bother posting the graph, but the elevation charts are all over the place on my GPS recording, but except for one dip down then up under an overpass, this section of the course was very flat.
Here’s an example of one time when I was running on a track. This kind of mapping error accumulates. I’ve realized if I want more precise workout feedback that it’s better for me to use a simple stop watch for track workouts or to turn off the GPS and use the calibrated footpod. It’s doubtful the tracks I run on are long, so it has to be that GPS isn’t perfect.
According to my Garmin, during the Philly race I ran the first three miles in 8:18, 8:21 and 8:13. Not that I’m not capable of running those paces, but I didn’t on Saturday morning. I ran this race as part of an 18 mile training run. I ran 5 miles before the race started then planned on running the race at around goal marathon pace. I was running by feel (had my arm warmer covering my watch, but I have it on vibrate for the mile laps), and I knew I wasn’t running that pace. The timing mats had me running the first 5k in 27:18, which averages out to an 8:48 pace. Right on target.
Once we left Center City, my watch tracked much better with the course, although by then it was about 3/10 of a mile ahead of reality. I had something similar happen when I ran the NYC Half in March. My watch lost it in Central Park and rather spectacularly in Times Square. As much as I’d love to believe I ran a 4:40 mile through Times Square, it didn’t happen. I missed my goal for that race because I was depending on Garmin, and Garmin was all over the place for the first 8 or so miles. I thought was running much faster than I was. The good thing was that I realized I had a problem when I hit Times Square, and I gave up looking at the watch and ran by feel. This was the first time I’d tried it, and it was largely successful. I still missed my goal, but my second half of the race was right on target. My body knew better than the watch what pace to run.
My race in Philly went really well. I ended up running the last 5k faster than marathon goal pace (about an average of 8:28/mile) and faster than the first 10k. You can see from the RnR results page that I picked up speed after the 10k mark. It’s nice when this happens, especially since I’d run 5 miles ahead of the race and was feeling strong by what was about miles 15-18 for the day. I felt relaxed and comfortable — confidence boosting for my marathon in 6 weeks.
According to my Garmin, I ran 13.4 miles. While I didn’t fuss over my tangents and probably could have run them more efficiently, that isn’t what accounts for the excess 3/10 of a mile recorded by Garmin. It was watch error. And I’m telling you, while it is possible for a race course to be off due to human error, the vast majority of the time it is the correct distance, NOT what the GPS device says.
I used to want to believe the Garmin because it certainly puts my running ability in a more flattering light. But it’s not reality, and in the long run, it doesn’t serve me to deceive myself. It’s also better for me to not be so reliant on that little wrist-sized bit of technology. I’ve learned to trust myself and enjoy running more by staring less at the watch.
If you don’t believe me, go back and look at your own data. Do a little tough critical analysis. You can thank me later. 😉