anonymous / November 13, 2014
Talk to me for 2 minutes about bike training and you’ll find out that I’m a big proponent of the power meter. Power is independent of conditions (wind speed and direction, temperature, gradient) – “watts are watts” – so is a consistent measure of output on the bike. It’s not only great for training, it’s also great for racing – especially at the longer distances, since it lets you dose out your effort more evenly and save something for the run.
But the tool is not infallible. Lots of things can affect your ability to get power data on a ride: signal drop out between your power meter and your bike computer, dead battery, or – one that I haven’t experienced that often – properly setting the “zero offset” for the torque.
This is a technical detail, but an important one: the way my Quarq power meter works, it’s important that you occasionally calibrate what this offset is (there are a couple of ways to do this, which aren’t important for the point of this article) or you won’t get accurate numbers. They could be lower or higher than what you’re actually putting out, and the amount of inaccuracy could be a lot.
On a recent 100-mile Ironman prep ride with teammates, I found myself working hard to push 180 watts, which is normally 15-20 watts lower than my conservative Ironman race pace. I was struggling to figure out why – was it that I was still recovering from a nasty cold virus I had picked up a few weeks before? Was it that my fitness wasn’t where it should be? I started questioning myself and whether I should even be doing this upcoming race.
I began to get suspicious, though, when my heart rate data showed that I was working within my general Ironman zone and that my average speed was also about where I would expect on a course that I had ridden numerous times before. Moreover, my teammates weren’t crushing me and leaving me in their dust. So I asked one who normally races around the same speed as I do what she was putting out. “185W,” was her answer, “and you’re pulling away from me.”
So taking all those other factors – heart rate, speed, comparable athletes, and finally my own perceived level of exertion – into account, I had to conclude that what was wrong was the power meter. At >the next gas station stop for liquids, I took the time to use the calibrate function on my Garmin computer, and sure enough on the ensuing stretch of road when I went back to the same perceived level of exertion, I saw that I was doing 215-220 watts – a little higher than I should have been doing.
The lesson: tools are great, but don’t be a slave to them. Sometimes the best tool is your experience as an athlete and what your body is telling you on the day. Even avid data geeks need perspective every now and then.