Carry on your marathon, there'll be food when you are done
Lay your GPS to rest, don't you cry no more -- Kansas, sort of
During my first marathon in 2007 I trained using the Nike+ shoe pod system as my distance-measuring method. However inaccurate it may have been (any variation from one's calibrated pace resulted in variations in distance of a few hundred meters), this system did wonders for my motivation and need for detailed data. Upon resuming my training a year later, I came to realize very quickly that electronic items using battery technology have a limited lifespan (i.e. batteries were dead). I needed to either 1) sink $30 into a replacement shoe pod or 2) get something better. Fortunately I was starting my training right around Christmas of 2008 and received from my in-laws a Garmin 205 as a gift (also known as the greatest Christmas present I've ever received, save for the giant tub of Legos I got when I was 2).
The GPS watch is a wonderful training tool. It's far, far more accurate than tools like Google Maps. Data is not only tracked, but is later searchable with varying degrees of granularity. It can be uploaded to the internet and shared. It does all sorts of cool stuff. I love my watch for training. I wear it for every training run I go on.
I'm also extremely hesitant to run in races wearing my GPS watch.
The first race that I ran with my GPS watch was the Cleveland Marathon in May 2009. For those unfamiliar with Cleveland, it's flat, doesn't have a whole lot of tall buildings, and borders a lake. All of these things should allow for pretty accurate GPS data, as a GPS watch locks onto multiple (at least five, according to my watch) satellite signals in order to accurately determine one's location. Within two miles of starting the race, my watch was off by more than half a mile (see image above).
This wasn't much of a concern early on in the race -- there were mile markers all along the way, so I could just ignore my watch for the most part. Throughout the race I just ignored my watch and carried on, knowing I still had a very long way to go. I caught up to the 3:30 pace group that I had planned to run along with at mile 21 and cruised with them on auto-pilot for three miles. With a few miles to go, I pulled ahead, knowing I would beat my goal time and PR.
With about a mile to go (according to my watch), I started to kick. My watch screeched at me, telling me I was done (AMATEUR TIP: don't set up a marathon race, just an open-ended run; then your watch won't tell you that you're finished). Annoyed, I turned my watch back on and continued along my way, feeling my legs start to grind. A block before the final turn a despicable, horrid human being told me that I'd turn the corner and see the finish line. Having no idea how much further I had to go (thanks, stupid watch), I trusted him.
I turned the corner and strained to see ahead -- the finish line was nowhere to be found. The crowd was thin, not indicative of a finish line. I ran another 0.6 miles before reaching the finish line, and was absolutely miserable. In my defense, I had already crossed the finish line in my mind, thanks to GPS. I also was supposed to be able to see the finish line when I turned the corner, thanks to advice from Lying McLiarson. Neither of those things were true.
Doing the math and staying rational about your watch being inaccurate is hard to do after an hour of running. After three hours, it's fucking impossible. In my next marathon, I wore a simple stopwatch -- if the GPS signals in downtown Cleveland weren't good, there was no way I was trusting the signals in Manhattan. I was probably right in doing so, but being accustomed to the hit-and-forget nature of the GPS, I missed a number of mile markers and had inaccurate mile splits. Train like you race, I suppose.
When I ran DC last spring I wore the GPS, but I did so running the race for fun -- with no plans to PR and no real goal in mind other than enjoying the race. (The watch turned out to be rather accurate, even with a quarter mile underground section of the course.) My next race, I'll likely wear the watch again -- but I won't be relying on it for any data on how much further I have to go.
The next time I'm trying to PR or hit any sort of qualifying time, I'll leave it at home.
What, if anything, do you use to track your distance? What are the limitations that you're aware of?